phabricator: add the phabdiff data structure This holds all the data about a commit, and is passed to the differential.creatediff API. Differential Revision: https://phab.mercurial-scm.org/D7044

phabricator: add the phabchange data structure These store data about individual files in a commit. Differential Revision: https://phab.mercurial-scm.org/D7043

phabricator: add the phabhunk data structure These store the actual diff data (for UTF-8 text files anyway) and are equivalent to hunks in a patch file. Differential Revision: https://phab.mercurial-scm.org/D7042

phabricator: add the DiffChangeType and DiffFileType constants These are used in Phabricator change objects. There are more values but so far as I can tell we don't need them. Differential Revision: https://phab.mercurial-scm.org/D7041

help: adding a help category to narrow and remotefilelog commands Differential Revision: https://phab.mercurial-scm.org/D6998

rust-cpython: drop self.borrow_mut() in favor of PySharedRef wrapper

rust-cpython: drop self.leak_immutable() in favor of PySharedRef wrapper

rust-cpython: add safe wrapper representing shared data borrowed from PyObject PySharedRef is a tempoary wrapper around PySharedRefCell. It provides safe functions for each shared data. $shared_accessor implements a safe method to construct PySharedRefCell. This allows us to add more than once PySharedRefCell to a Python object.

rust-cpython: move $leaked struct out of macro It wasn't easy to hack the $leaked struct since errors in macro would generate lots of compile errors. Let's make it a plain struct so we can easily extend it. PyLeakedRef keeps a more generic PyObject instead of the $name struct since it no longer has to call any specific methods implemented by the $name class. $leaked parameter in py_shared_iterator!() is kept for future change.

rust-cpython: store leaked reference to PySharedState in $leaked struct I want to move it out of the macro, and allow multiple sharable objects per PyObject.