BUG : fix imports during sphinx build

added scikit and sub-modules to mock list

closes #13
Merge branch 'tacaswell-fix_doc_build' into python-packaging-11

tcaswell created a fix for the import problems during Sphinx builds
replace with system-independent method to find elements.h5 file
fix all sphinx complaints about bad section underlining, resolve as **BOLD** text instead, docs now build with no errors