Only including prepared API docs

Our sphinx-apidoc made it so all our pydocs were included in our built
documentation. This is great, except that those documentation dumps are
completely unreadable. Dropping the sphinx-apidoc call in favor of including
specific autodoc pages we've prepared.

Made some revisions to stem.version's documentation and including that to
start.
Revised API docs for stem.exit_policy
Revised API docs for stem.descriptor.reader
Adding toctree declarations

Sphinx gives a warning saying "document isn't included in any toctree" if all
*.rst documents aren't included in a toctree somewhere. I'm not using a toctree
as our primary form of navigation so it doesn't really make sense, but it's
easy enough to make a contents page off to the side that satisfies sphinx.
Revised API docs for stem.descriptor.export
Revised API docs for stem.descriptor
Revised API docs for stem.descriptor.server_descriptor
Revised API docs for stem.descriptor.extrainfo_descriptor
Revised API docs for stem.descriptor.networkstatus
Line wrapping pydoc clauses

I had been avoiding line wraps in :var:, :param:, and :return: entries to avoid
confusing the spinx compiler but on reflection it's output is uneffected when
we indent the following line.

Just wrapping the lines that were really unweildy rather than going for a
strict eighty character width. Sorry
lines-of-code-must-be-shorter-than-my-iphone-screen zelots.
Revised API docs for stem.descriptor.router_status_entry
Revised API docs for stem.util.enum
Revised API docs for stem.util.conf

The utility's header was pretty sucky so rewrote it to better exemplify how
this module should be used.
Revised API docs for stem.util.connection
Revised API docs for stem.util.str_tools
Revised API docs for stem.util.log
Revised API docs for stem.util.proc
Revised API docs for stem.util.system
Revised API docs for stem.util.term
Revised API docs for stem.util.tor_tools