Add tides computation as boundary condition for MITgcm

[apetronio-OGS]

Starting from template matlab scripts, based on matlab library "tmd", I provied a first re-coding in python, taking advantage of the pyTMD library pyTMD, source code available here.
There are 2 py files, set_bc_grid and set_bc_tides: the first one to prepare the boundary files from the MITgcm grid, and the latter for the computation of the tideal constituents. Typical usage is to run the first and then the second.
The inputs can be provided by means of a sonfiguration file in json format, or as arguments of the function via command line.
At this stage there is a debug flag to print out some variables, and to check them against the old tides computed by dr. S. Querin for the case of "run_160p_AZAL_HR_for_grid".
Respect to the matlab outputs there are small to large discrepancies due to two main factor:

1. The tides database are different:

• the old one is no more avialable for download, but still present in OGS database, it has 24° resolution
• the new one is provided by Oregon State University, 12° resolution, named as TPXO10, available in bynary format "TPXO10-atlas-bin" or in a netCDF format as "TPXO10-atlas-netcdf";
• To refer to this model in OGS publications please use the citation:
  Egbert, Gary D., and Svetlana Y. Erofeeva. "Efficient inverse modeling of barotropic ocean tides." Journal of Atmospheric and Oceanic Technology 19.2 (2002): 183-204.

2. The implementation of the tidal driver are different.