Update to rust master

The `bitflags` macro didn't initially add a Copy impl so we had to do
that manually. Now it does and it was conflicting with the our explicit
implementation.
Merge pull request #47 from tomassedovic/bitflags-build-fix

Update to rust master
Instruct Mac OS users to switch to the 1.5.x branch

The default `hg` checkout of libtcod uses the 1.6.0 version, which is
we're currently not compatible with.
Merge pull request #48 from tomassedovic/set-libtcod-version

Instruct Mac OS users to switch to the 1.5.x branch