Basic fromproj4 works, except need better handle when unprojected (longlat and latlong)

Also just need to expand to more projection name, datum name, and
ellipsoid name definitions, and also additional special parameters.

After that, test, and move onto from_wkt()...

pycrs/datums.py

@@ -0,0 +1,5 @@
+
+class WGS84:
+    proj4 = "WGS84"
+    ogc_wkt = "WGS_1984"
+