NF - added signal-to-noise function to stats
Changed function name of SNR to signal_to_noise
changed function name and cleaned up some grammar
added gain parameter and made suggested changes to documentation
removed gain and fixed some errors
Added gain and updated documentation
added simple test for snr function
added more tests for snr function
Allow time format and scale strings to be case-insensitive
added Msun alias for solar mass unit
Implement an IPAC table writer

This is based on discussions in #833 and and #1143.
@taldcroft
@keflavich
Please use this pull request to suggest your changes.

closes #833
fix itendation errors in documentation
modified for the suggetions on the pull request
improve formatting as the taldcroft suggestion
fixes a small bug that prevented changes in the comment symbol on writing

closes #790
Multiplication/division of TimeDelta, updating documentation and tests.
Comparisons of Time and TimeDelta
implement the changes dicussed on the issue tracker in github
return the identation as much as possible to @taldcroft original design
Add __truediv__ for python 3, as well as one-line doc-strings