Support TranslateArray

See issue #6.
Share implementation of Translate and TranslateArray
Let requests encode URL parameters

Rather than using urlencode from urllib to build the URL with
parameters, we can just pass the parameters into requests.get().

This makes for less code and less string-manipulation, at the cost of
making TranslatorMock slightly more complicated.
Support DetectArray

See issue #6.
Merge pull request #13 from wjt/master

Support DetectArray and TranslateArray