rust-sdl 0.3.5: namespaced enums.

The fix should be at most mechanical, hopefully, but this will surely
affect virtually *every* user code, so the version number has been
bumped to inform the necessary renaming rules. The rules are:

* Every variant which name shares a common word with the enum has been
  renamed to omit that word. This also applies to the partial match.
  Examples:
  - `DefaultRepeatDelay` -> `RepeatDelay::Default`
  - `AppMouseFocusState` -> `AppState::MouseFocus`
  - `InitTimer` -> `InitFlag::Timer`

* As an exception, variants named `No<enum name>` has been renamed to
  `<enum name>::None`.

* There are no public reexports of enum variants except for `Color::RGB`
  and `Color::RGBA`. Those two are commonly constructed by the user code
  and deserves a shortcut.