Make weights keyword work in LEVMArLSQFitter
Fix extra white space in empty line
Expand documentation for fill_values

fixes #2080
[skip ci]
Merge pull request #2900 from hamogu/fix2900

fitting with weights does not work
Fix typo [skip ci]
Merge pull request #2904 from larrybradley/typo

Fix typo [skip ci]
Merge pull request #2902 from hamogu/fix2080_2

Expand documentation for fill_values
Allow format specificiers as Column format strings & deal with masked values.
Also refactored the string tests, and added regression test against formatting
of np.float32, etc.  Because masked values now are OK: [closes #1026]