Add function to send completed surveys to the backend API.

Includes classes for Response and Survey objects.

This commit fixes issue #8
Move JSDoc comments to be above functions
Change sendSurvey to take success and error callback functions.
Use these callbacks for handling control flow for success, error, and
timeout conditions.
Set default timeout for survey submission to 4s.
Style fixes (function declaration, constants, JSDoc types, semicolons).
Remove use of for-in loop and make sure variables are declared with
"var".

See
https://google-styleguide.googlecode.com/svn/trunk/javascriptguide.xml?showone=for-in_loop#for-in_loop
for details on why for-in is bad.
Remove semicolons from end of function declaration for Response and
Survey.
Fix use of SERVER_URL constant in sendSurvey function.
Simplified for loop just use length directly.
Remove extra semicolons (thanks @meacer).
Merge pull request #12 from christhompson/send-survey

Add function to send completed surveys to the backend API.