Added typescript typings to support serialized pub-sub messages.

[wayneparrott]

Added typescript typings to support publishing and subscribing to serialized messages.

• index.js - converted createMessageObject() to constrained generic returning less ambiguous MessageType instead of Message.
• node.js - added isRaw to _validateOption()
• node.d.ts - converted createPublisher() & createSubscription() & deletePublisher() to generic constrained to MessageTypeClassName. Improves type inferencing. Similarly modified SubscriptionCallback.
• package.json - refactor dtslint test stage of the test script to test-ts script
• publisher.d.ts - converted Publisher class to generic constrained to MessageTypeClassName.
• test/type/main.ts - updated tests; added new tests

Fix #706

[coveralls]

Coverage remained the same at 91.183% when pulling b10313ea1d05c8bff26bd19a36237c7b0e222e1b on wayneparrott:develop into 25282cefbb3b1bb4df252d96efeb92396bfcca05 on RobotWebTools:develop.