Update broken links: "LICENSE.txt" gets a full-path link, and don't point to "http://crate.io" anymore.

RST readme files don't render properly on PyPI when there is a broken link, and the link to "LICENSE.txt" was a local reference and, hence, is regarded as broken.  This PR provides a full path link to LICENSE.txt.  Hopefully this will make the readme render properly on pypi.  See the `toolz` page on pypi here:

https://pypi.python.org/pypi/toolz/

Interestingly, the readme renders just fine in the preview of the next generation PyPI (just as it also displayed fine on crate.io):

https://preview-pypi.python.org/project/toolz/

Next, https://crate.io has been mysteriously taken over by http://crate-technology.com , although they do redirect links back to pypi.  This PR changes links to point directly to pypi.python.org instead of crate.io.  So much for trying new, shiny things!