[pfff] php_stdlib/Makefile should not assume `~/pfff`

Summary:
... instead, if no `PFFF_HOME` is provided, the `CURDIR`
 Makefile variable should allow the pfff root to be located.

Test Plan:  cd data/php_stdlib/ && make

Reviewers: pad

Reviewed By: pad

Differential Revision: https://phabricator.fb.com/D1533127
[pfff] php: recognize binary integer literal syntax

Summary:
 `0b101` syntax is valid in PHP5.4 (see http://php.net/manual/en/language.types.integer.php).
 Fortunately, that happens to be a subset of the binary literal int syntax supported by int_of_string
 (http://caml.inria.fr/pub/docs/manual-ocaml/libref/Pervasives.html#VALint_of_string)

Test Plan:
 - included test
 - make tests

Reviewers: pad

Reviewed By: pad

Subscribers: jwatzman

Differential Revision: https://phabricator.fb.com/D1533124

Tasks: 5012598
[pfff] php: recognize async lambdas

Summary:
 ... this does the bare minimum of parsing, and still has all
 the issues that pfff has with recognizing normal lambdas (i.e. not
 being able to understand typehints, variadics, etc).

Test Plan:
 - included changes to `tests/php/parsing/short_lambda.php`
 - make test

Reviewers: jwatzman, pad

Reviewed By: pad

Subscribers: jan

Differential Revision: https://phabricator.fb.com/D1533210

Tasks: 5050674