Support HHVM/Hack 3.29, add migrations

This release:

• supports and requires HHVM/Hack 3.29
• supports typed user attributes, including 'unused use statement' linter fixes
• marks EditableList::fromItems() as <<__Deprecated>>, in favor of EditableList::createNonEmptyListOrMissing() which is equivalent, but clearer about the behavior
• adds hhast-migrate --is-refinement, replacing is_int() with is int and similar expressions.

This release also includes hhast-migrate --ltgt-to-ne and --hhvm-3.28-to-3.29, replacing <> with !=, which was added in v3.28.7

There have been several changes to the AST in this release; the most significant are:

• classes might not have a name (if the file being parsed is PHP; anonymous classes are not supported in Hack)
• attributes are no longer a unique node type; instead, <<Foo>> is a constructor call to Foo (this is part of the 'typed user attributes' feature)