Added urlopen, urlretreive, and urllib2.urlopen

I added additional functionality to the interface.  We can now call
urlopen from urllib_tuf, urlopen from urllib2_tuf, and lastly
urlretreive from urllib_tuf... We may need to make multiple of these
functions as it appears there is some variability to the parameter list,
but this is a pretty simple copy-pasta exersize that should be done as
needed
Merge branch 'master' of github.com:PoppySeedPlehzr/gemsontuf