dillon1000/react

[be] Split files into directories

Moves _some_ files from HIR into new top-level directories. To not make 
@gsathya's life a pain I left the files he's touching alone, but I moved some 
others. My intent is to have something like this: 

* Babel/ - code for the Babel plugin, though ideally this actually gets split 
into a separate package and the compiler itself is AST in, AST out w no Babel 
dep. 

* HIR/ - the core HIRFunction, HIR and related data types, plus the HIR 
construction and printing, HIR visitors. 

* Inference/ - the core inference passes that operate on the HIR, including type 
inference, reference effects, alias analysis, mutable range analysis, etc. I'll 
let @gsathya  move these files when at a good stopping point. 

* ReactiveScopes/ - inference relating to reactive scopes, 
constructing/printing/codegenning ReactiveFunction 

* SSA/ - enter/leave SSA and eliminate redundant phis 

* Utils/ - every project needs a place to put stuff that doesn't fit into the 
other categories, this is ours. 

This leaves just index.ts at the top level, and overall feels pretty tidy. Not 
too tedious to figure out where anything goes, hopefully.