Format 1A7 – update to Snow Crash v0.16.0

This PR brings updated Snow Crash v0.16.0 that implements Format 1A7. 

However there are two tension points (not really introduced here)

1. Naming of C interface functions
2. The very existence of the CHANGELOG.md

### ad 1
The Snow Crash C interface function names are, at least, confusing. This is the most apparent when it comes to source maps. This is apparent when it comes to the names of variables and functions [around this code](https://github.com/apiaryio/redsnow/pull/38/files#diff-10f89a34ff7ff6c3f42db75936ffa3acR172). 

I do not see a better way than to revisit @alikh31 work, and to rename these functions in the Snow Crash (and here) before it will be adapted by a broader audience.

### ad 2
What is the point of separate change log file when we are using GH Releases? Perhaps @abtris can elaborate. Otherwise I do not see any benefit in duplicating the release informations...
`sc_reference_handle_payload`