Refactor include_columns and exclude_columns
remove n_data_cols
Make more use of colnames property
Add table of built-in cosmologies, other minor documentation cleanups.

* closes #1147
Remove table.cols, unneeded comments, unneeded DictLikeNmy
remove index for columns - since all columns are always there, no separate index is needed
remove leftover comment
Fix sphinx warning, add note about doc update

* Extra space before code block in Built-in Cosmologies section
  of index.rst
* Add warning to parameters.py to update the documentation table
  when adding a new cosmology
change the way null values are handled in IPAC table writing

fixes #1344
add strip to remove extra whitespace in python3
add missing import statement
simplify new test to not to depend on votable and its unicode handling
remove try-except that could mask other errors
Fix decoding of platform name.
Fix py.test 2.4.0 on Python 3.1
Merge pull request #1530 from mdboom/tests/encoding-is-none

py.test cannot run if sys.stdout.encoding is None
Merge pull request #1531 from mdboom/tests/fix-pytest-on-py3.1

Restore compatibility with Python 3.1?
Merge pull request #1527 from aconley/cosmo_builtin_docs

Add table of built-in cosmologies, other minor documentation cleanups.
Merge pull request #1533 from astrofrog/fix-catch-warning-issue

Make sure the list of modules being iterated over cannot change during iteration
Change interpretation of lists in Table.__getitem__ (closes #274)