[Sphinx] URL to source code is not rewritten

[pd0wm]

When generating a sphinx documentation with the github-tools extension the URLs to source files is not rewritten and still contains an underscore (e.g. '_modules/....').

An example can be found at: https://pd0wm.github.io/spectral/spectral.core.source.usrp_n210.html

[pd0wm]

Oops. Did not see: #14

Maybe this should be added to the documentation.