Use URLSearchParams for paramsObject

[cailyncodes]

Implements feature in issue #88.

This pull request changes the object of paramsObject from a native JS object to a URLSearchParams object. The actual implementation is simple -- most of it is removing code because URLSeachParams handles everything. The bulk of the changes are changes to the tests because this is a breaking change.

[ernsheong]

Unfortunately the extra dependency makes this unappealing I suppose.