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.
Add an option to guess the start of data for reading CDS files
Add cds_malformed.dat test file
Add docs for setting data_start to 'guess'
Updated CHANGES.rst
Add comment line in test referencing issue numbers
Update equivalencies.rst

Removed (nearly) repeated text.  I kept the most recent additions.
Corrections to ensure Distance can be compared.  Closes #2206
Merge pull request #2241 from taldcroft/cds-malformed

Add an option to guess the start of data for reading malformed CDS files
Update construct_table.rst

Fixed typo.
fixed AiryDisk2D model
updated changelog
updated changelog
Updated AiryDisk2D model docs
Merge pull request #2252 from larrybradley/patch-2

Update construct_table.rst
defined module-level constant for AiryDisk2D model; fixed bug with peak-pixel amplitude
changed AiryDisk2DKernel input parameter from width to radius to match AiryDisk2D model