Module system, usability, documentation

This is a big release since it provides a full interactive evaluation story. You'll need to buy into it by using the module and def... macros instead of fn and local though!

• Added last and count to aniseed.core.
• More tests.
• Better internal looping functions based on the run! function.
• Update nvim.lua and fennel.
• Ensure fennel.path matches lua.path.
• Full module system, documented in the readme.
• deftest module included as part of module system. Test suits are even nicer!
• A bunch of scripts to help you fetch deps, compile Fennel, run tests and embed Aniseed within your plugin for runtime use.
• Mappings by default when you're in a Fennel buffer. I hope they're inoffensive 😬
• More documentation.
• One easy step to allow you to write your Neovim config in Fennel.

I hope you enjoy! It's been a lot of hard work, I hope it allows people to go out and make all sorts of amazing plugins that run faster and are easier to maintain and extend into the future 🎉