Compare performance of oxipng vs optipng

This adds a script to automate this process and add it to the README.
I'll just run it manually after a version release, for now.

Closes oxipng#81

Author: Josh Holmer

.gitignore

@@ -2,4 +2,5 @@ target
 *.bk
 .DS_Store
 *.out.png
-/.idea
+/.idea
+/node_modules

README.md

@@ -91,3 +91,34 @@ Other contributions (such as improving documentation or translations) are also w
 ## License
 
 Oxipng is open-source software, distributed under the MIT license.
+
+## Benchmarks
+
+Tested oxipng 0.18.3 (compiled on rustc 1.25.0-nightly (0f9c78475 2018-01-17)) against OptiPNG version 0.7.6 on Intel(R) Core(TM) i7-4980HQ CPU @ 2.80GHz with 8 logical cores
+
+
+
+Benchmark #1: ./target/release/oxipng ./tests/files/rgb_16_should_be_grayscale_8.png
+
+  Time (mean ± σ):     121.5 ms ±   7.9 ms
+ 
+  Range (min … max):   113.4 ms … 145.0 ms
+ 
+Benchmark #2: optipng ./tests/files/rgb_16_should_be_grayscale_8.png
+
+  Time (mean ± σ):     241.3 ms ±   5.0 ms
+ 
+  Range (min … max):   234.4 ms … 249.4 ms
+ 
+Benchmark #1: ./target/release/oxipng -o4 ./tests/files/rgb_16_should_be_grayscale_8.png
+
+  Time (mean ± σ):     289.7 ms ±  24.0 ms
+ 
+  Range (min … max):   251.1 ms … 332.5 ms
+ 
+Benchmark #2: optipng -o 4 ./tests/files/rgb_16_should_be_grayscale_8.png
+
+  Time (mean ± σ):     944.2 ms ± 127.5 ms
+ 
+  Range (min … max):   861.5 ms … 1278.4 ms
+ 

README.template.md

@@ -0,0 +1,96 @@
+# Oxipng
+
+[![Build Status](https://travis-ci.org/shssoichiro/oxipng.svg?branch=master)](https://travis-ci.org/shssoichiro/oxipng)
+[![Version](https://img.shields.io/crates/v/oxipng.svg)](https://crates.io/crates/oxipng)
+[![License](https://img.shields.io/crates/l/oxipng.svg)](https://github.com/shssoichiro/oxipng/blob/master/LICENSE)
+
+## Overview
+
+Oxipng is a multithreaded lossless PNG compression optimizer. It can be used via a command-line
+interface or as a library in other Rust programs.
+
+## Installing
+
+Oxipng can be downloaded from the [Releases](https://github.com/shssoichiro/oxipng/releases) link on the GitHub page.
+
+Oxipng can also be installed from Cargo, via the following command:
+```
+cargo install oxipng
+```
+
+Alternatively, oxipng can be built from source using the latest stable or nightly Rust:
+```
+git clone https://github.com/shssoichiro/oxipng.git
+cd oxipng
+cargo build --release
+cp target/release/oxipng /usr/local/bin
+```
+
+The current minimum supported Rust version is **1.20.0**. Oxipng may compile on earlier versions of Rust,
+but there is no guarantee.
+
+Oxipng follows Semantic Versioning.
+
+## Usage
+
+Oxipng is a command-line utility. Basic usage looks similar to the following:
+
+```
+oxipng -o 4 -i 1 --strip safe *.png
+```
+
+The most commonly used options are as follows:
+* Optimization: `-o 1` through `-o 6`, lower is faster, higher is better compression.
+The default (`-o 2`) is sufficiently fast on a modern CPU and provides 30-50% compression
+gains over an unoptimized PNG. `-o 4` is 6 times slower than `-o 2` but can provide 5-10%
+extra compression over `-o 2`. Using any setting higher than `-o 4` is unlikely
+to give any extra compression gains and is not recommended.
+* Interlacing: `-i 1` will enable [Adam7](https://en.wikipedia.org/wiki/Adam7_algorithm)
+PNG interlacing on any images that are processed. `-i 0` will remove interlacing from all
+processed images. Not specifying either will keep the same interlacing state as the
+input image. Note: Interlacing can add 25-50% to the size of an optimized image. Only use
+it if you believe the benefits outweight the costs for your use case.
+* Strip: Used to remove metadata info from processed images. Used via `--strip [safe,all]`.
+Can save a few kilobytes if you don't need the metadata. "Safe" removes only metadata that
+will never affect rendering of the image. "All" removes all metadata that is not critical
+to the image. You can also pass a comma-separated list of specific metadata chunks to remove.
+`-s` can be used as a shorthand for `--strip safe`.
+
+More advanced options can be found by running `oxipng -h`.
+
+## Library Usage
+
+Although originally intended to be used as an executable, oxipng can also be used as a library in
+other Rust projects. To do so, simply add oxipng as a dependency in your Cargo.toml,
+then `extern crate oxipng` in your project. You should then have access to all of the library
+functions [documented here](https://docs.rs/oxipng). The simplest
+method of usage involves creating an
+[Options struct](https://docs.rs/oxipng/0.13.0/oxipng/struct.Options.html) and
+passing it, along with an input filename, into the
+[optimize function](https://docs.rs/oxipng/0.13.0/oxipng/fn.optimize.html).
+
+## History
+
+Oxipng began as a complete rewrite of the OptiPNG project,
+which was assumed to be dead as no commit had been made to it since March 2014.
+(OptiPNG has since released a new version, after Oxipng was first released.)
+The name has been changed to avoid confusion and potential legal issues.
+
+The core goal of rewriting OptiPNG was to implement multithreading,
+which would be very difficult to do within the existing C codebase of OptiPNG.
+This also served as an opportunity to choose a more modern, safer language (Rust).
+
+## Contributing
+
+Any contributions are welcome and will be accepted via pull request on GitHub. Bug reports can be
+filed via GitHub issues. Please include as many details as possible. If you have the capability
+to submit a fix with the bug report, it is preferred that you do so via pull request,
+however you do not need to be a Rust developer to contribute.
+Other contributions (such as improving documentation or translations) are also welcome via GitHub.
+
+## License
+
+Oxipng is open-source software, distributed under the MIT license.
+
+## Benchmarks
+