Added new Matlab scripts

[arango]

Several Matlab scripts were added:

• 4dvar/obs_extract.m: Extracts data from input data assimilation observations NetCDF file at the requested time interval (days) and creates new observations NetCDF files at such intervals. This script may be used to generate input observation NetCDF files for the Ensemble Kalman Filter (EnKF) from 4D-Var observations files. That is, they can be used for 3-dimensional First Guess at Appropriate Time (3D-FGAT) data assimilation with EnKF.

• utility/daynum.m: Converts requested date (year, month, day, ...) into a serial date number. It uses the Proleptic Gregorian Calendar, which extends backward the date preceding 15 October 1582 with a year length of 365.2425 days. It is similar to Matlab function datenum but differs on the origin (day=0), which corresponds to Mar 1, 0000.

• utility/dayvec.m: Converts a given date number as computed by daynum to a date vector (year, month, day, hour, minutes, seconds). It is the inverse function to daynum. It is equivalent the native datevec function.

• utility/inferno.m: A 256 colormap by Nathaniel J. Smith and Stefan van der Walt.

• utility/magma.m: A 256 colormap by Nathaniel J. Smith and Stefan van der Walt.

• utility/plasma.m: A 256 colormap by Nathaniel J. Smith and Stefan van der Walt.

• utility/viridis.m: A 256 colormap by Eric Firing.

• utility/yearday.m: Given (year, month, day) this function computes the day of the year.

I also updated 4dvar/obs_read.m, landmask/uvp_masks.m, and netcdf/roms_metadata.m scripts.