Improve "positions.rst" to confirm GitHub #26
Remove extraneous "::" hiding testsetup:: block
Remove useless call to ''.join()
Remove no-op lambda, at a cost of more if-else's
Rename JulianDate._utc() to ._utc_tuple()
Add JulianDate._utc_float()
Switch to UTC for minutes from satellite epoch

I had misread the first paragraph of AIAA 2006-6753 II.E.
Make initial position examples more thorough

Show explicitly how each major kind of position can be generated from a
solar system object, and from a star object, instead of leaving that
implicit or for users to piece together.  Also, switch to a dictionary
list instead of a bullet list and rename the documentation links to
"Read more" since even I myself did not see them for about a minute when
the links were the names of the three kinds of object!
For GitHub #26, fix satellites and documentation

Not only does this make satellite behavior and its documentation
actually agree, and provide a way for satellite calculations to avoid
having to compute the JPL position for the Earth just to determine how a
satellite is positioned relative to a place somewhere else in the local
coordinate system of the Earth, but we also go ahead and expand the
examples at the top of the positions.rst documentation to cover all
basic coordinates someone could want to compute.  You know, just in case
they don't bother reading any farther than the summary at the top.
Merge branch 'issues/26'