Add flat prior option to binom_conf_interval.  Fix bugs with scalars.

* Add flat prior option to binom_conf_interval and binned_binom_proportion
* Fix bug where jeffreys prior crashed when given scalar values of k.
* Added unit test for flat prior and for scalar jeffreys prior.
* Update docs and put in 0.4 changelog
Fix typo (fucntion)
Comments from @kbarbary

* Fix docs
* Try to return input shape more faithfully.  Add some unit tests
  of that behavior.
Change the way shapes are handled in binom_conf_interval

* Rather than explicitly reshape the output, treat scalars
  as a special case and let the ufuncs deal with broadcasting.
  Doesn't seem to change any aspect of the output.
Fixed Gaussian2D model for cov_matrix input
Added change log entry for #2199
Added regression test for #2199
Changed Gaussian2D model rotation to increase counterclockwise
Updated regression tests for #2199
Updated documentation for Gausian2D model
Updated change log entry for #2199
Updated docs to display the covariance matrix as a matrix
Explicitly raise NotImplementedError for _repr_latex on Quantity arrays
Merge pull request #2157 from aconley/binom_flat

Add flat prior option to binom_conf_interval.  Fix bugs with scalars.
Added HTML reader to io.ascii
Added reader to existing system
Implemented write() functions
Changed write() method to use XMLWriter
Moved bs4 import, added provision for comments in Splitter
Accidentally put import in class rather than in method process_lines