Added default blank values for credentials

This will allow the service to return an error instead of the enigmatic NilClass error when credentials are omitted.

Modified to convert non-string license key values

v14.4.3

Update avatax.gemspec

Reformatted for distribution as gem

This release includes some minor fixes, as well as a reformat of the libraries and samples such that they might be made available through RubyGems.

Service version 14.4 release 1

v14.4.1

Typo fix