Query GVP volcanoes by name

[jwellik]

Usage:

from vdapseisutils.data import gvp_volcanoes as gvp

volc = gvp.get_volcano("Shishaldin") # retrieve a volcano by name
volc = gvp.get_volcano(lat, lon, radius) # retrive volcanoes with a radius from lat,lon

returns a dictionary of "name", "lat", "lon", "elevation"