Tweak sphinx config for wheezy build

Should now build (even with math support!) under Wheezy, although it
does involve loading a metric ton of javascript to support the math
stuff...

debian/control

@@ -3,7 +3,7 @@ Maintainer: Dave Jones <dave@waveform.org.uk>
 Homepage: http://picamera.readthedocs.io/
 Section: python
 Priority: extra
-Build-Depends: debhelper (>= 8), python-all (>= 2.7), python-setuptools, python3-all, python3-setuptools, python-docutils, python-sphinx (>= 1.0.7+dfsg-1~)
+Build-Depends: debhelper (>= 8), python-all (>= 2.7), python-setuptools, python3-all, python3-setuptools, python-docutils, python-sphinx (>= 1.0.7+dfsg-1~), libjs-mathjax
 Standards-Version: 3.9.3
 X-Python-Version: >= 2.7
 X-Python3-Version: >= 3.2
@@ -33,7 +33,7 @@ Description: Pure Python interface to the Raspberry Pi's camera module.
 Package: python-picamera-docs
 Architecture: all
 Section: doc
-Depends: ${sphinxdoc:Depends}, ${misc:Depends}
+Depends: ${sphinxdoc:Depends}, ${misc:Depends}, libjs-mathjax
 Description: Documentation for the Python interface to the RPi's camera module.
  picamera is a library for working with the Raspberry Pi's camera module from
  within Python without having to resort to subprocesses. The majority of the

debian/rules

@@ -18,3 +18,5 @@ override_dh_installdocs:
 	python setup.py build_sphinx -b html
 	dh_installdocs
 
+override_dh_sphinxdoc:
+	dh_sphinxdoc -Xmathjax

docs/conf.py

@@ -70,8 +70,16 @@ def __getattr__(cls, name):
 
 # -- General configuration ------------------------------------------------
 
-needs_sphinx = '1.4.0'
-extensions = ['sphinx.ext.autodoc', 'sphinx.ext.viewcode', 'sphinx.ext.intersphinx', 'sphinx.ext.imgmath']
+extensions = ['sphinx.ext.autodoc', 'sphinx.ext.viewcode', 'sphinx.ext.intersphinx']
+if on_rtd:
+    needs_sphinx = '1.4.0'
+    extensions.append('sphinx.ext.imgmath')
+    imgmath_image_format = 'svg'
+    tags.add('rtd')
+else:
+    extensions.append('sphinx.ext.mathjax')
+    mathjax_path = '/usr/share/javascript/mathjax/MathJax.js?config=TeX-AMS_HTML'
+
 templates_path = ['_templates']
 source_suffix = '.rst'
 #source_encoding = 'utf-8-sig'
@@ -90,9 +98,6 @@ def __getattr__(cls, name):
 pygments_style = 'sphinx'
 #modindex_common_prefix = []
 #keep_warnings = False
-imgmath_image_format = 'svg'
-if on_rtd:
-    tags.add('rtd')
 
 # -- Autodoc configuration ------------------------------------------------