Add documentation describing Planck13 and massless neutrinos
If an IOError or ValueError occur when trying to check if the 'header' variable is a valid pathname then go ahead and assume it is not a pathname
Raise an ImportError rather than call sys.exit() when astropy can't be imported from a source checkout; also add a _teardown_log function to undo Astropy's logging setup--otherwise subsequent attempts to 'import astropy' in the same session lead to strange exceptions.
Fix a typo (which never came up due to the except: pass) and add the PR number to the changelog.
Restore the original log level after each of these tests; this still didn't solve the issue but it seems worthwhile
Fixes the tests in question by not assuming that the default log level is INFO
Define degree, arcmin and arcsec Unicode characters in the latex preamble
Fix docstring format in astropy.modeling.polynomial.Legendre1DModel.deriv
provided indications to build the PDF documentation
Improved error message for WCS when incorrect number of arguments is passed.
Merge pull request #1374 from mdboom/coordinates/angle-to-string-scalars

Angle.to_string() returns a 0-d array with dtype=object
Fix angle doc examples after #1374
Merge pull request #1399 from taldcroft/angle-object-docs

Fix angle doc examples after #1374
Merge pull request #1388 from mdboom/coordinates/angle-unit-parsing

Fix angle/unit parsing
Change syntax for assigning new row values in add_row()

This fixes a problem that comes from the following numpy bug when assigning
to a row that has object-type fields:
```
>>> a = np.array([('1',)], dtype=[('x', 'O')])
>>> a[0] = a[0]
ERROR: ValueError: Setting void-array with object members using buffer. [IPython.core.interactiveshell]
```
Merge pull request #1394 from astrofrog/wcs-improved-error-arguments

Improved error message for WCS when incorrect number of arguments is passed
Merge pull request #1403 from taldcroft/fix-1403

Fix problem adding a row to a table with object-type field(s)
Merge pull request #1395 from mdboom/wcs/shape

WCS conversion functions accept 2xN and Nx2 arrays
Merge pull request #1393 from migueldvb/docs

Fix building PDF documentation
Merge pull request #1362 from nhmc/Planck13_doc_update

Add documentation describing Planck13 and massless neutrinos