Add docs/* to .gitignore.
Add a docs task to mix.exs and a docs target to the makefile.
Make Travis grab exdoc and build the documentation.
Preload the Flect.Compiler.Syntax.Preprocessor module too.
Correct the type spec for Flect.Application.start/2.
Define Flect_Cross if the compiler is built as a cross compiler.
Lots of API documentation.