Attempting Categorization

Taking a stab at categorizing the tools. While I appreciate the list, it has never been particularly useful for me to browse the mixed bag alphabetically; Typically, I am in need of a particular type of tool, and categorization would be more helpful to me.

Also, since it was giving me eyebleed from all of the headers and listing each title twice, I turned them all into RST Definition Lists.

Some opinions were made (monitoring, CollectD/Ganglia/Sensu, the Other category). Sue me.

More bikeshedding could be had, but not terribly useful (chars-per-line, etc)
Fixing missing indentation

Somehow three lines either were missed, or somehow mucked up in the copy.
fixing merge conflict by adding in a new tool, but preserving the original intent of categorizing the tools
a little more cleanup and consistency
Merge branch 'master' into patch-2
Merge pull request #688 from gwaldo/patch-2

Attempting Categorization of Tools and changed formatting