DOC: update bug report page for scipy.org and docs.  Closes gh-74.
MAINT: moving the Citing page from scipylib to scipy.org main page.

Closes gh-72.
MAINT: update Install page (WinPython link, remove Python 3.x note).

Most distributions now supports Python 3.x (as do all package managers),
and the rest should follow soon-ish, so better to delete the note on this
topic.

Closes https://github.com/scipy/scipy/issues/4010
Merge pull request #77 from rgommers/maint

Several fixes and maintenance updates.