Formatting issues in the documentation.

[1uc]

This page has issues with formatting links and code-blocks: https://bluebrain.github.io/nmodl/html/contributing.html

This page fails to display Latex formulas: https://bluebrain.github.io/nmodl/html/notebooks/nmodl-sympy-solver-cnexp.html

This page fails to display latex formulas and has a IPython prompt that's empty: https://bluebrain.github.io/nmodl/html/notebooks/nmodl-odes-overview.html