Improve Clojure highlighting.

I've differentiated between control-structury things and builtins. While there
is rarely a true difference in these things because of the way Clojure works,
it makes sense to highlight them differently. All of the desktop editors make similar
decisions with their Clojure lexers. My reason for doing it is that it allows
for more complex highlighting. I'm not sure if all of the things in the keyword
list make sense there, but they do at a glance. I'll look more closely when I
get to using this and send another pull request with any tweaks.

Clojure's keywords (like :foo) were being highlighted as tags. That doesn't make sense and is
inconsistent with, for example, the Ruby mode. You don't want to highlight tags
the same as keywords in some cases because you can end up with pretty keywords
and hideous HTML tags. I've switched those to be highlighted as atoms as per
the Ruby mode.

A few of the indent words were not being detected because they were being
concatenated without trailing spaces. I fixed that.