Intersphinx

Added rst labels to tools docs. Generate new objects.inv file with:

$ make html

after posting to readthedocs, should be able to add this to conf.py in sphinx:

intersphinx_mapping = {'bedtools': ('http://bedtools.readthedocs.org/en/latest/', None)}

and generate url links to bedtools command documentation from sphinx docs with:

:mod:`BEDTools.map <bedtools:map>`

That last bit needs to be tested, but is based on the intersphinx section of:

http://read-the-docs.readthedocs.org/en/latest/features.html