Remove backticks around None. This is not a ref
Fix formatting in docstring for dates
Merge pull request #3521 from jenshnielsen/more_doc_fixes

DOC : More doc fixes
DOC : fix main-page tags

<pre> -> <tt> for inline markup.
Merge pull request #3543 from tacaswell/fix_mainpage

DOC : fix main-page tags
Merge pull request #3585 from matplotlib/v1.4.0-doc

merge V1.4.0-doc into v1.4.x