Attempting Categorization of Tools and changed formatting

Apologies for not taking this in stages, but I couldn't leave it half-done.

I took 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)