Adds user-agent to request headers.
Make GraphBuilder _execute concat url and query string

GraphBuilder _execute was calling the _del with a query param, which
was refactored out because other callers had all been appending the
query to the url param before calling.
support multiple related parameters, closes #25
fix offset issue, closes #24
version bump
Merge pull request #27 from Bowery/sjkaliski-fix

fix offset issue, closes #24
Merge pull request #21 from housejester/jde-user-agent

Adds user-agent to request headers.
support pagination, closes #22

fix

fix
merge in #28 and version bump
Merge pull request #23 from Bowery/sjkaliski-next

support pagination, closes #22