Quality of the core

[bminixhofer]

Currently the core is still largely in the state it was during prototyping. While abstractions are good and the code is clean documentation is missing in the internals.

So the key issue is:

• Improving documentation of the internals.

Besides that, there are some cleanups needed such as:

• Thinking about the distinction between byte and char indices and when should be converted between them (Use byte indices in Rust core #21)
• Better error messages for wrong binaries (Better error if binary does not match version #20)
• Profile & reduce allocations (use more iterators...) (related Some methods should return iterators #28)
• Check opportunities to use Cow<str>
• derive(Clone) all the (public) things.
• Replace to_string with to_owned when converting from &str to String.
• Making rayon optional behind a feature flag.

[drahnr]

Adding to the list of nice to haves:

• avoid hindrance of cloning - current the regex engine used is not clone
• provide more iterators and avoid allocations
• use Cow<&str> where feasible

[bminixhofer]

Thanks, I added them to the list along with some other things.