Rewrote to work with webapi-parser

Major changes (BREAKING):

• Rewrote to work with webapi-parser (#31);
• 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 (now inferred automatically);

Minor changes:

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