Use consistently dots at the end of bullet points in 'Main Features' (#2055)

Author: yvonnefroehlich

pygmt/__init__.py

@@ -12,10 +12,10 @@
 
   - Easy handling of individual types of data like Cartesian, geographic, or
     time-series data.
-  - Processing of (geo)spatial data including gridding, filtering, and masking
+  - Processing of (geo)spatial data including gridding, filtering, and masking.
   - Allows plotting of a large spectrum of objects on figures including
-    lines, vectors, polygons, and symbols (pre-defined and customized)
-  - Generate publication-quality illustrations and make animations
+    lines, vectors, polygons, and symbols (pre-defined and customized).
+  - Generate publication-quality illustrations and make animations.
 """
 
 import atexit as _atexit