Support passing query and headers to fission functions

[erwinvaneyk]

Currently only the default input is mapped to the body of fission functions.

To support passing inputs to the headers and query of the fission function invocation, we need to add the following mappings in the fission runtime environment.

Inputs:

• headers : JSON object (map) mapped to HTTP headers
• query : JSON object (map) mapped to query parameters.

Optionally, each entry in the headers and queries could also be map to support multiple headers/query params with the same key, but that is not a terrible thing not to support.

@soamvasani

[erwinvaneyk]

Fixed in #91