Rework using webapi-parser

[postatum]

Major changes:

• Reworked to work with webapi-parser;
• New dev dependency: webapi-parser;
• Dropped dependency: xtend
• First argument to a default exported function is now an array of webapi-parser.EndPoint objects;

Minor changes:

• Updated dependencies' versions;
• Switched to const/let instead of var;

Making a release:

• Release dependencies PRs;
• Bump major version and make a release;

PR depends on:

• Rework using webapi-parser osprey-router#31

To test the PR locally with all the reworked Osprey sub-dependencies, use this Makefile.