honor api base url
Merge pull request #9 from seletskiy/master

Api BaseUrl.Path is not honored by `do` method
test for #9
Merge pull request #10 from cryptix/testForPath

test for #9
Use net/url vor baseUrl and QueryValues
using bitly's simplejson to handle complex, dynamic json responses
fixed tests
remove variadic interfaces where we don't need them
added FormPost