Hyperlink the shiznit out of config-reference.rst

* Add a short section about where to set configuration options
* Move "command line switch" column to 2nd column instead of last, so it's next to the config file version of the config key name
* Specify config option data types as data types and not "combined by" functions
* Describe data types more completely in config docs
* Obsessively link every config key in the reference page to its full description, wherever that is
* Add some other random internal hyperlinking

Hosted on my Dropbox: https://dl.dropboxusercontent.com/u/360865/mrjob_docs/index.html

Most of the action is here: https://dl.dropboxusercontent.com/u/360865/mrjob_docs/guides/configs-reference.html

Fixes #650, #649, and #648.