Initial stable release; performance improvements, additional migrations

Today we're releasing version 1.0, as HHAST is now in regular use at several companies, and the codebase has been largely stable since v0.4, which was released in November.

This release:

• significantly improves the performance of typechecker-based migrations, such as the call-time-pass-by-reference migration
• supports the safe_array, safe_vector_array, and experimental no_fallback_in_namespaces (available in nightly builds) typechecker options
• adds a migration for the no_fallback_in_namespaces option
• adds a generic 'add-fixmes' migration, which adds HH_FIXME comments as required; this is a last resort migration and should be used rarely

Lifecycle

• 1.x releases will be supported throughout the lifecycle of HHVM 3.24, and will continue to target HHVM 3.24.
• when HHVM's AST changes, 1.x will be forked from master, and master + 2.x will target future releases of HHVM
• once 1.x diverges from master, any major changes (e.g. new features, performance improvements) should be made against master, then once committed, if desired, also landed to the 1.x branch