Enhancement (DELETE) and Bug fixes (around POST response)

1. fetch(), check for negative response to raise HALNavigatorError is not too late?
   I feel it should be called before processing the response body 

2. PostResponse can have properties, hence (__call__ != fetch )
   Hence, implemented to return properties

3. DELETE method is similar to POST from Navigator perspective (non-idempotent) 
   However, it is responsive could be interesting at times. 
   Reused logic from POST to support DELETE
   Hence,  renamed PostResponse to HALResponse and create to post for clarity
   In order to provide backward compatiablity, I created alias (create) to post

4. HALNavigator should not allow POST if the uri is templated, the check for templated_uri 
   was missing. Created wrapper function to re-use for all methods - GET/POST/DELETE

TODO:
Tests for DELETE method