Document existing kernel file routines

The docs are really basic, mostly copies of what is already in the source.
Functions that are not implemented are not mentioned. Also clarified a
couple places in the source itself.
Miscellaneous documentation clarifications and cleanups
Convert arguments to monospaced type

This makes them easier to distinguish from surrounding text,
especially in a bulleted list.
Change userspace.md extraneous files extension

.lab is for SPASM only.
Replace HTML with better Markdown in memory.md
Remove emphasis HTML tags in memory.md, replace with Markdown
Merge pull request #40 from thirtythreeforty/docs

Docs