updating to all 'full_name' to all currencies.

all currencies have 'full_name', even if full_name == name.
attr_reader :full_name, list_from_full_name method
set global for attr_reader of full_name
added tests for full_name, and renamed GBP fullname to Pound Sterling
Merge pull request #11 from superscott/master

adding 'full_name' for all currencies