Specify lower-bound Sphinx version

Hieroglyph with Sphinx 1.0 will error out:

    Exception occurred:
      File "/usr/local/lib/python2.7/dist-packages/hieroglyph-0.6.5-py2.7.egg/hieroglyph/builder.py", line 46, in init_templates
        warn=self.warn)
    TypeError: init_themes() takes exactly 2 arguments (4 given)

some old distributions provide an outdated sphinx, but because hieroglyph only depends on *Sphinx* `pip` or `easy_install` will consider that the requirement is fulfilled when installing hieroglyph, then it'll blow up at runtime.

Sphinx 1.1 may work, I have not checked.