Add common alias verbose (V) (#550)

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.

Author: weiji14

pygmt/helpers/decorators.py

@@ -36,6 +36,18 @@
         color : str
             Select color or pattern for filling of symbols or polygons. Default
             is no fill.""",
+    "V": """\
+        verbose : str
+            Select verbosity level [Default is w], which modulates the messages
+            written to stderr. 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""",
     "W": """\
         pen : str
             Set pen attributes for lines or the outline of symbols.""",