Improve general API

[Meziu]

This PR comes with a lot of changes to the API for all modules (related to #102), loosely following the standards. The changes include:

• Moved gfx and romfs to the services module
• All ctru-sys derivative enums have members set to the ctru-sys equivalent (and a blanket From implementation)
• get_* methods have been renamed
• Massive renames for enums and structs (especially in cam)
• Fixed name repetitions in enum variants and module members
• fixed cam enums being wrongly used as bitflags!
• usize -> u32 convertions have been solved with .into() where possible
• Small documentation improvements (a full-blown doc PR will come)

This is a massive PR when counting changed lines, but in reality it's mostly just cleanup and refactoring.