Use pry for troubleshooting
Improve the way responses work

- Determine client response status using Suretax::API::Response.
- Add handling for partially successful posts.
- Provide TaxAmount class for ease of use, particularly coverting Floats to Integers to avoid floating point bugs.
Move suretax_wrap_response into SuretaxSpecHelper
Add test coverage for "invaid request" API response
Use existing test hash data instead of JSON string
Use Hash#fetch in Api::Response params

This will raise errors on missing keys
Move Api::TaxAmount testing out of Api::Response
Remove redundant RequestSpecHelper include
Make Api::Response tests read better
Remove redundant RequestSpecHelper and spacing from test
Use suretax_wrap_response instead of hardcoded string
Create objects for all parts of the API response

- Added Group for 'GroupList', accessible via Api::Response#groups.
- Added Tax for 'TaxList', accessible via Api::Group#taxes.
- Currency amounts in Tax are TaxAmount instances.
Remove VCR dependency
Use suretax_wrap_response instead of string literal
Use parallel directory structure in tests
Shorten unecessarily verbose Response#success?
Remove redundant leading namespaces

Suretax:: etc is not necessary within the Suretax module
Fix test for truthiness in Api::Response

And use Rspec idiomatically
Use Monetize (Money) gem for currency amounts

- Parse input using Monetize.parse
- Register custom USD currency with six decimal places as US6
Change class name from TaxAmount to generic Amount

This class works with all money amounts, so its name should not be specific to taxes.