Add Makefile, currently configured for ATTiny45

[semi-simple]

For people who would rather use the command-line than an IDE, I made this Makefile.

Currently it only works with the raw AVR chips rather than full arduino boards, but it should be easy to adapt. It's a good starting point and template for whoever wants to use the command line with this project.

[kalymos]

Sorry for replying too late, but I didn't have the courage to do it before.
I preferred to focus on integrating bio patches for Japanese consoles, creating the wiki, a map manager, and a tutorial as comprehensive as possible.
Now that I've finished all that, I have the courage to reply.
I think you have a very good idea, but personally, for the moment, I don't feel like getting involved.
Especially since I don't plan on publishing a Makefile where I can choose all the different possible compilation combinations.
Aside from these personal considerations.
In the current state of the code, we're supposed to be able to compile without using Arduino; the MUC.h file contains all the necessary register pointers and clock management.
It would be really interesting to use gcc for compilation with cross-compilation tools; to me, it makes much more sense in the case of a Makefile.
And also, we want to be able to do it on different operating systems.

Thanks anyway for your interest in the project, and I hope you won't be too disappointed by my vision ;)

[semi-simple]

Yes, this all makes sense, making this production-quality and supporting all the options etc would be a lot more work. I needed this for my own use anyways, as I really don't want to use any IDE, so this was not a waste of time. You could potentially consider putting it in some "extras/" directory or something so that people have an easier starting point if they want to go this route (including with GCC support), but they might just be able to find this PR on GitHub anyways.

Thanks for the great project!