Initial run-tests.sh

This file comes from Michiel Brentjens; I have modified it slightly to
suit PINT better, but at this point it produces *many* pylint errors,
not to mention all the nosetest failures.
Tweak to work better with virtualenv

Running nosetests directly uses the system python; in a virtualenv you
need to use "python `which nosetests`" to pick up all the proper
packages.
Fixed easy pylint warnings
Set up pylint RC file

This is the right place to add custom rules about what is okay. In
particular I think we may need to add something there to suppress all
those warnings about astropy units; it would also be good to turn on
variable name warnings, but we'd need to let it know that variables like
dX and i are kosher.
Initial Sphinx setup
Added some sphinx modules
Raise exceptions if startup fails

If the PINT variable is not set or the SPICE data files are not
available, raise an exception so that the tests fail.
Tell wget to continue if timestamp the same
Fixed a few doctests
Converted to unit tests

Now uses a class to wrap up all test methods as separately-runnable
tests that each start from a clean instance prepared by running the
setUp method.
Ported tests and fixed bug

Converted tests of TOA reading; tests revealed a bug in the handling of
TOAs without DDM values. Fixed.
Fix minor bugs
Check for current version of tempo2

My version of the general2 plugin doesn't support certain options, so it
simply doesn't produce those outputs. This should not appear to be a
test failure for pint.
Updated instructions

Noted that PINT needs TEMPO and TEMPO2 for testing, and that it needs
the PINT and TEMPO environment variables to be set.
Deactivated astropy messages

Unfortunately there isn't a "right" way to compensate for the fact that
pylint can't tell what members astropy modules have. Numpy has the same
problem. This is a hack.
Remove unnecessary python before scripts

This was a hack to make it work in a partial virtualenv. Better to just
install nose and pylint in the virtualenv.
Cleaned up doc structure
Replaced all print statements with log messages
Doc edits
Doc improvements