working on doc tickets
starting rewrite of install docs
Adding docs about installing in develop mode.
interim ci
modified release docs.
adding new url for downloads
adding source build to travis-ci
Merge pull request #268 from pastephens/docs

updating travis file
Adding  method in W that calls WSP class for convenience and elegance. Related to issue #226
Fixing doctest of towsp method by including type(wsp)
Fixing doctest of towsp method by including isinstance(wsp, ps.weights.weights.WSP)
Merge pull request #269 from darribas/issue226

Adding towsp method in W