Documentation style guidelines

[avivace]

Some guidelines on the style we should adopt/apply suggested by @Bananattack :

• use consistent formatting;
• any new information / rewrites should be written clearer than the original;
• keep things concise and short;
• don't repeat information like register/mode descriptions, reference/backlink to existing information instead;
• present things as clear rules/definitions first, then explain or elaborate after.

Related issues: #55

[ISSOtm]

What's the status on this?

[avivace]

What's the status on this?

WIP in the wiki