The ROXML library handles boolean XML true false fields
http://roxml.rubyforge.org/rdoc/classes/ROXML/ClassMethods/Declarations.html
However, in the code base there is a lot of duplicate predicate methods
that could be eliminated by simply adding a '?' to the end of
xml_accessor e.g.
by setting:
xml_accessor :active?, :from => 'Active'
this would eliminate:
def active?
  active.to_s == 'true'
end

This PR would possibly break code that relies on an unset attribute to
be false e.g.
Currently, if active is not set it will return false if the predicate
method from above has been created.
After the PR it will return nil.
Moreover, after this PR there is no longer a getter method e.g. 'model.active'.
Currently, a call to 'model.active' would return the string "false" or "true". After the PR
it will be an undefined method.
Implemented AccessToken endpoint for OAuth token management: renewal and disconnect. Closes #50
Use respons.plain_body in AccessToken Service
Merge pull request #51 from pavelpachkovskij/master

Use response.plain_body in AccessToken Service
0.0.7 release
fix BillPayment REST_RESOURCE
fix PaymentMethod, PurchaseOrder, VendorCredit REST_RESOURCE path
Was using incorrect REST endpoint for PurchaseOrder. Fixes #53
Release
Merge pull request #52 from pavelpachkovskij/master

fix invalid REST_RESOURCE path
Line is an array in Payment model
Merge pull request #55 from pavelpachkovskij/master

Line is an array in Payment model
Catching HTTP 503 Service Unavailable
Adding support for linking payments to an invoice
Threading through initializer arguments
Adding discount line detail option to Line
Merge branch 'master' into catching_service_unavailable
Merge pull request #58 from harvesthq/linking_payments_to_invoice

Adding support for linking payments to an invoice
Merge pull request #59 from harvesthq/fixing_initialize_on_certain_models

Threading through initializer arguments
Merge pull request #60 from harvesthq/catching_service_unavailable

Raise Quickbooks::ServiceUnavailable upon 503 error