Improving CLI boot times

[kddnewton]

There is a fair amount of code in Syntax Tree that doesn't get executed unless you're treating it like a library. This includes everything under the lib/yarv directory, the parser translation, and a lot of the visitors.

We should be more judicious with when we load code. Because of the dual nature of this project (CLI and library) the CLI suffers worse boot times for every line of code added to the library that doesn't immediately impact formatting.

A combination of autoloading and/or nesting requires more deeply into the files that need them should do the trick, but profiling and experimenting will be required. The benchmark we should be improving is

$ stree format -e 0

That should be as fast as we can make it.

[kddnewton]

Updated now with a lot of autoloading.