Installation section rewrite

Each extension has its own configuration and installation section, and these sections don't really follow a standard. We need a standard.

OS

The main issue is Windows versus Unix. Currently this is done in many ways so it's rather confusing.

For details, see: http://markmail.org/message/c7hz3yycg4mvyje5

PECL

Whether or not an extension is in PECL is another issue, as is worrying about if it moved to or from PHP core.

TODO

Essentially this task involves three steps.