Add common alias verbose (V)

[weiji14]

Description of proposed changes

Select verbosity level [Default is w], which modulates the messages written to stderr. See https://docs.generic-mapping-tools.org/6.1/gmt.html#v-full. Choose among 7 levels of verbosity:

• q - Quiet, not even fatal error messages are produced
• e - Error messages only
• w - Warnings [Default]
• t - Timings (report runtimes for time-intensive algorthms);
• i - Informational messages (same as "verbose=True")
• c - Compatibility warnings
• d - Debugging messages

Cherry-picked from #546.

Fixes #

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst.
• Write detailed docstrings for all functions/methods.
• If adding new functionality, add an example to docstrings or tutorials.

[seisman]

FYI, the GMT experimental long options use verbosity and spherical for -V and -j (https://github.com/GenericMappingTools/gmt/blob/master/src/gmt_init.c#L383), while GMT.jl uses verbose and spheric_dist | spherical_dist(https://www.generic-mapping-tools.org/GMT.jl/latest/#GMT.grdmask).

[weiji14]

I would definitely prefer 'verbose' for V, it's similar to most command-line arguments.

As for 'j', I've merged the PR already, but could make a quick change. The GMT.jl documentation actually points to http://docs.generic-mapping-tools.org/latest/gmt.html#j-full (i.e. capital J) rather than the proper link at https://docs.generic-mapping-tools.org/latest/gmt.html#distcalc-full (notice the distcalc in the link).

[seisman]

Yes, I also prefer verbose for -V.

For j, I'm OK with the names. It depends on if we want to keep consistent with other GMT projects.

[seisman]

FYI, I believe the GMT server is up.