New branch for documentation, with an initial skeleton.
Changed `make doc` target to re-use Sphinx cache.

To do this, the document root and autogenerated bro script docs
are rsync'd in to Sphinx's working directory instead of a plain
recursive copy.  There are still some index files that are auto
generated on each build and will trigger Sphinx to re-build them
since it thinks they changed, but overall the build is much faster
this way.

One limitation of this is that old files in the Sphinx work dir
don't automatically get cleaned up (e.g. if you remove some static
documentation from the /doc it will still be in
build/doc/sphinx-sources).  So a `make docclean` or at least
`make broxygenclean` is needed at least in that case.  (For now,
rsync --delete isn't the right answer since the destination of
the autogenerated stuff overlaps with the document root, the separate
rsyncs end up clobbering each other.)
Moving submodules.
Initial commit of the scripting user manual.
Additions, spelling corrections, prior to addition of custom scripts to be used in the User Manual.
Merge branch 'topic/documentation' of ssh://git.bro-ids.org/bro into topic/documentation
Merge remote-tracking branch 'origin/master' into topic/documentation

Conflicts:
	doc/index.rst
Rewriting explanation of detect-MHR.bro to match recent changes to lookup_hostname_txt()
Exploration of the connection record data type and corresponding btests.
Beginning exploration of network centric data types, starting with subnets.
Improve description of built-in types

Added more information on operators and literals.
Merge remote-tracking branch 'origin/master' into topic/dnthayer/lang-docs
More updates to built-in types document
Merge remote-tracking branch 'origin/master' into topic/documentation
Merge remote-tracking branch 'origin/master' into topic/documentation
Merge remote-tracking branch 'origin/master' into topic/dnthayer/lang-docs
Document undocumented attributes
Local variables.  Baselines and data_type_local.bro btest-able script.
A short discussion of variables versus values in the section on Local Variables.
Vector declarations and explanations, including btests