Merging install logic with the rest

Currently, the document is sourced from two places: the first part is new, written by @dagolden (in wikidoc) and describes mostactions and arguments; the second part was written by Ken, and is a straight copy from Module::Build's docs. In particular, the workings of options is spread in a weird way.

How do we iron this out? Also with regards to some of the issues mentioned in #6.
