Main converter for AT

Summary: This plumbs together the other bits, to actually read, munge,
and re-write a PHP file. Still a couple features missing, notably doing
this nicely over a directory and actually being able to specify
loose/strict, but it at least is vaugely usable at this point.

Reviewed By: @ptarjan

Differential Revision: D1700788

Signature: t1:1700788:1417468009:ec149ff55ddba4e4a96c77ce123e199cc28d9d5f
Makefile for AT

Summary: So external folks can build it :) Requires pfff installed via
opam, and ocaml 4.

Reviewed By: @int3

Differential Revision: D1702193

Signature: t1:1702193:1416877798:fc14915958b9b6ddfe2121b3e4b80e155dd8989d