Fixed file mode for reading pickle tiles
Added function to properly convert strings to long doubles
Update toa.py

Corrects two bugs: the first given by using "is" instead of "==" to compare a variable and a string, and the second given by using the attribute "tdb" for an astropy column instead of the times it contains.
Merge pull request #7 from matteobachetti/patch-3

Update toa.py.  Thanks, Matteo!
Massive number of changes to get table-based timing model calculations to work
Merge pull request #4 from nanograv/master

New merge from nanograv