Initial implementation of calculation of astronomical Julian Date.
 * Added 'to_julian_date()' to Timestamp
 * Added 'to_julian_date()' to DatetimeIndex
 * Added tests for both methods.

TST: Stylistic changes to to_julian date tests.

API: DatetimeIndex.to_julian_date now returns a
     Float64Index.
TST: Moved to_julian_date tests from
     pandas/tseries/tests/test_julian_date.py into
     pandas/tseries/tests/test_timeseries.py
DOC: Added mention of to_julian_date functionality
     to doc/source/release.rst and v0.14.0.txt

DOC: Added docstring to Timestamp.to_julian()

TST: Change to use PANDAS testing rather than numpy.

DOC: release.rst/v0.14.0.txt updates