The default role is no longer used. Introduced :stack: role.

- Also used :title-reference:, and other markup cleanup.
Made :word: the default role.
Renamed stream words

- `forward` -> `get`, `current@` -> `i`, and `valid?` -> `i?`.
- Similar for words that contain these strings.
- renamed prefix `get-` to `read-`.
Added documentation, mainly about naming conventions.