Adding php -l linter

Summary: Adds a linter that checks php files for syntax errors using php -l

Test Plan:
Add a section to your .arclint file similar to:

"php": {
  "type": "php",
  "include": "(\\.php$)"
}

Then run arc lint on a php file with a syntax error.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: epriestley, jacobwalker0814, Korvin

Differential Revision: https://secure.phabricator.com/D10370