2014-07-30  Gerrit Holl  <gerrit.holl@utoronto.ca>:

	* pyatmlab/collocations.py:

	(CollocatedDataset):

	- Initialise start_date and end_date based on the start and end dates
	for the constituent datasets.

	* pyatmlab/dataset.py:

	(StationaryDataset):

	- Added class that will super to any ground-station dataset

	* pyatmlab/math.py:

	(linear_interpolation_matrix):

	- Calculate transformation matrix for linear interpolation between two
	  grids

	* pyatmlab/physics.py:

	(p2z_hydrostatic):

	- Added two missing params to docstring