General purpose reformating and rewording in (a few places). This should
also make markdown linting happier.
Prefer back-ticks wherever useful and use `console` for code blocks to
be executed on terminal.
Also, update references links wherever possible (including update from
'http://' to 'https://').
Document that `fasd` is now bundled with prezto (19990c80252a588ef0983fe16c2f001391775af8) and that it's a fallback to a manually installed version (04bfb5131b63c626062af535a1c429f9ff303ca4).
