Version substitution 724

Fixes #724

I have tested this by setting `version = '0.1.2-99-ge08b10f'` in `conf.py` and seeing an error:

``gettingstarted/tutorial/vagrant-setup.rst:202:ge:vagrant-setup``

without this fix, and no error with this fix.
This and the comment about putting all the code inline are what stumped me for a while. You get `PicklingError`s. The closest thing I've found for an explanation is:

> To be used in a document, the custom filter needs to be installed somewhere that Sphinx can import it while processing the input files.

from http://sphinxcontrib-spelling.readthedocs.org/en/latest/customize.html#custom-word-filters