Improves the output formatting of units.  The old method always used scientific notation, so you'd get string things like `u.min` displaying as `6 * 10^1 s` rather than just `60 s`.  The new method just builds on Python's "general purpose" float format `g`.
Add a test
Update docs to reflect new formatting
Fix ordering of output from compose so it is ordered by abs(x.scale) (more meaningful than ordering by the string sort).
Fix LaTeX spacing of unit format output
Fix double space problem in default formatting
Update test for new LaTeX formatting
Remove extraneous parentheses in unit formatting.
Merge pull request #913 from mdboom/unit/better-formatting

Improves the output formatting of units.