Added more explicit example of printing without any format.
LaTeX uses the more usual form of the word (instead of the more correct form with chi): this makes it easier for people to find information ("uncertainties python latex" does not yield any result in Google!).
Added unit test that should pass but currently fails.
More precise docstring.
Merge branch 'master' into fix_print_nan
Consistently transformed "LaTeX" to the more usual (albeit incorrect) form with an X (instead of a chi): this should help Google searches on formatting numbers with uncertainties in LaTeX.
Merge branch 'master' into fix_print_nan
Added more complete test for NaN nominal value.
Added more NaN printing tests.
Marked places (with !!!…) where a NaN nominal value can break the formatting.
Comment on exponent convention added.
Merge branch 'master' into fix_print_nan

Conflicts:
	uncertainties/__init__.py
Better comment.
Better comment.
Added todo marks (!!!!…) in places where a NaN nominal value of standard deviation should be used.
Fixed test
Nicer (commented out) information message.
Clean handling of NaN when formatting (before, max() was used, with a result that may not have been defined). Updated the todos to the new situation for a NaN nominal value: exp_ref_value is now None instead of NaN.
Removed obsolete todo.
Added NaN±… formatting test.