Changing FITS table write function to have default value of Nan for float type cols
Changing default value for float columns from 1e20 to Nan in fits table write function
Changing the float comparison for filled value to np.allclose to enable Nan masking for float32 as well. Also added test cases for float64, and float32
Removing unnecessary comment
Fixing io docs links for #1221
Minor docs modifications
FITS_rec objects can be pickled with this patch
Small modifications to FITS_rec pickling, and tests added
Changing tests and adding changelog entry
Fixing pickling for python3.3
allow greater flexibility in CDS table reading
Permit any callable, not just a function, for format

For instance, a class that implements a `__call__` method is also fine.
minor tweaks in answer to comments to PR
Set default fill_value to 0
Merge pull request #2296 from bsipocz/fix_io_for_1221

Fixing io docs links for  issue 1221
fix 2315 by checking scale == 0
Merge pull request #1335 from hamogu/fix1335

io.ascii.cds does not implement some aspects of the CDS missing value specification
Add unit test for callable object format argument
Add changelog entry for #2313
Document that Table.format can accept a callable object