Improve Pretty Printer (apache#52)

* adds all binary ops

* various pretty printing improvements and some documentation

* implements + operator for doc (just does APP)

* refactoring and towards LLVM syntax

* more refactoring

* adds some pp tests

* adds if pp test

* adds some documentation to doc.h and the link to the original paper

* poor attempt at refactor to get mutual recursion

* commit

* mutual recursion here we go!

* complete mutual recursion. add missing pretty_print cases. print type information in let expressions

* messed up rebase stuff

* fix bugs introduced by rebase

* make code cleaner

* use ReasonML ref syntax

* refactor pretty printing

* linting

* linting

* linting

* linting

* python linting

* py linting

* py linting

* improves list and block semantics. adds regression tests. fixes C++ reference style

* most function names now follow C++ style

* cpp linting

* type annotations and tests

* cpp linting

* improve doc.h documentation format