Overhaul documentation

[mazziechai]

Currently, the library's documentation is sparse, and when it does exist, it's simply a copy paste of the Aphelion specifications.

At minimum, basic documentation should be provided for everything in the library, including internals, to ease development in the future. Public interfaces must include more information, such as appropriate usage.

Modules to document

• helper
• instruction
• interrupt
• io
• nibble
• registers