Added hashes

added hashes for SteamApp and SteamAchievement
made SteamApp, SteamAchievement hashable

Added __eq__ to allow the items to be properly hashable
Moved "__eq__" and "__hash__" to main implementation of SteamObject so any two API objects can be compared.
Improved __hash__ in each inheriting class to prevent ID collision cases causing wrong matches.
Merge pull request #10 from smiley/pr/7

Merged PR #7