Rework using webapi-parser

[postatum]

Major changes:

• Reworked to work with webapi-parser;
• New dev dependency: webapi-parser;
• Dropped dependency: xtend;
• Now depends on mulesoft-labs/router#router-engine instead of blakeembrey/router#router-engine. Former repo contains latter repo changes merged on top of latest updates of pillarsjs;
• Second argument to Router.<METHOD> functions is now an array of webapi-parser.Parameter instead of uriParameters schema;
• Dropped RAMLVersion option;

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 raml-path-match#14

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