[hack] Tweak IDL => hhi generation

Summary:
Fix one issue in the JSON reader wrt namespaces, clean up the
Makefile, other minor tweaks.

Test Plan: "make update"

Reviewers: pad, julienv, glevi

Reviewed By: pad

CC: neal, ps, erling

Differential Revision: https://phabricator.fb.com/D1130023

Task ID: 3537742
Wire up HNI generation for stdlib

Summary:
Wire my shell script to generate stdlib files from the new HHVM
HNI extensions into the pfff makefile for stdlib.

Test Plan: "make update" generates reasonable-looking files.

Reviewers: pad, julienv, glevi

Reviewed By: pad

Differential Revision: https://phabricator.fb.com/D1132534

Task ID: 3537742
Partially write "make stdlib"

Summary:
I give up on this, I don't think this is going to get us to a
maintainable state over just hand-rolling things from here on out, but
didn't want to lose this work.

Test Plan: "make stdlib"

Reviewers: pad, julienv, glevi

Reviewed By: pad

Differential Revision: https://phabricator.fb.com/D1132887

Task ID: 3537742