Merge pull request #170 from ahey/master

Add exchange_rate and home_total_amount to the invoice model
Add global_tax_calculation to Invoice model.
Merge pull request #171 from michaelcheung/global_tax_calculation

Add global_tax_calculation to Invoice model.
Update README.md

Added link to contributors
fix custom field xml accessor typo
Merge pull request #172 from waelchatila/master

fix custom field xml accessor typo
Add global_tax_calculation to all transaction entities that use it.
Merge pull request #173 from michaelcheung/global_tax_calculation

Add global_tax_calculation to all transaction entities that use it.
Support sandbox mode
Merge pull request #174 from arthurchui/sandbox-mode

Support sandbox mode
0.1.6 release
Throw ServiceUnavailable for HTTP 504s as well as HTTP 503s
Catching invalid XML responses and returning a helpful error
Merge pull request #176 from harvesthq/invalid_xml_responses

Invalid xml responses
Added Quickbooks::Forbidden for HTTP 403
Connect the params argument from fetch_by_id to do_http_get
Merge pull request #181 from benzittlau/master

Connect the params argument from fetch_by_id to do_http_get
Merge pull request #180 from arthurchui/error-401-403

Added Quickbooks::Forbidden for HTTP 403
0.1.7 release
Adding additional support for payment methods.