added driver d_std_obc.m

[arango]

Added a Matlab driver script d_std_obc.m to extract and write open boundary condtions standard deviations which are used in 4D-Var. This is just a template script that can be used to compute the error covariance standard deviation for open boundary conditions. As an example, they are extracted from the initial conditions standard deviation data.

I also corrected minor typos in the documentation of d_ssh_obs.m and d_sst_obs.m.