v0.18.0

GMT v0.18.0

Diff since v0.17.0

Closed issues:

• Register 0.16.0 (#347)
• grdimage shows strange lines (#357)

Merged pull requests:

• Alpha work (#353) (@joa-quim)
• Add a region argument ogrread (#354) (@joa-quim)
• Warn when kwarg options are not consumed. (#355) (@joa-quim)
• subscript in docs (#358) (@htyeim)
• Several changes to accomodate GMT breackages (#359) (@joa-quim)
• Try my GMT branch (#360) (@joa-quim)
• Try to download a nerwer gdal and use a test for it (#361) (@joa-quim)
• Contour var cont (#362) (@joa-quim)