changed met_functions to comply with pull request #81 regarding magnetic_declination and the magnetic_correction functions
Fixed vel functions and bettered the docstrings and comments
wrapped up the changes to vel functions for VEL3D and VELPT instruments
updated vel_functions to contain the numexpr's for vertical velocities.  Also updated the README.txt and cleaned up comments in do2_functions.
Merge pull request #100 from s-pearce/vel3d

CIDEVMI-1031 DPAs for VEL3D