Refer to the enum variants correctly

Enum variants are now by default scoped under the enum name itself.
Remove duplication in Console variant names

This renames `Console::RootConsole` to `Console::Root` and
`Console::OffscreenConsole` to `Console::Offscreen`.

The re-exported root console is still under `tcod::RootConsole` for backwards
compatibility and clarity.
Remove duplication in PathInnerData variants
Remove the `key_code` and `background_flag` modules

The reason we had them in the first place was not to pollute the tcod module
with all the enum variants. Now that they're scoped under the respective enums,
that's no longer necessary.

This is a breaking change.
Bump tcod-rs to version 0.2.0

Just to make the breaking changes a bit more apparent.
Merge pull request #39 from tomassedovic/namespaced-enumps

Namespaced enums