Update WGS84 module to reflect WGS 84 publication.

Documentation was added as well.  Some names were changed to refelct
the official names.  Other code that uses WGS 84 will need to be
updated to use the new names (for example, 'R0' is now 'a').
Update navpy to use new wgs84 naming convention.

Since the official wgs 84 parameters were implemented, some of the
doc-tests were adjusted to reflect the new numbers.  This is only
true for the earthrad function.  No other doctests were modified.