Support and require HHVM 3.26, relicense to MIT, experimental support for PHP

This release:

• is available under the MIT license
• adds support for - and requires - HHVM 3.26
• switches version numbering scheme to match HHVM
• has experimental support for PHP code
• adds the IComment marker interface to identify comment nodes
• improves detection of color support and interactive consoles in the CLI utilities

3.26 Requirement

This release of HHAST requires hh_parse from HHVM 3.26; as hh_parse is usually distributed with HHVM itself, HHVM 3.26 has been marked as a requirement in composer.json - however, if you deploy hh_parse separately, you can update independently.

Versioning and lifecycle

HHAST exposes Hack's AST - so, when changes are made to Hack's AST, HHAST itself must change. As such, it is likely that a new version of HHAST will be needed for each HHVM release. Because of that, we've decided to follow HHVM's version numbers for clarity.

The major and minor versions (3.26) will match the minimum version of HHVM required; the revision (.0) is independent for the HHAST.

For bugfixes and security updates, HHAST will follow HHVM's support lifecycle.