Added support for tdAddDevice, tdRemoveDevice and tdGetErrorString

tdAddDevice just adds an empty device with no name, protocol, device code, etc. Will add support for:
-tdSetName
-tdSetModel
-tdSetProtocol
-tdSetDeviceParameter
-tdLearn
Added support for tdAddDevice, tdRemoveDevice and tdGetErrorString

tdAddDevice just adds an empty device with no name, protocol, device code, etc. Will add support for:
-tdSetName
-tdSetModel
-tdSetProtocol
-tdSetDeviceParameter
-tdLearn
Update telldus.cc
Slight update, old uncommitted code.
Updated readme
Update readme.md
Added asynchronous calls to turnOn, turnOff, and dim, so as to not halt the node.js process while waiting for feedback from the Tellstick.
Merge branch 'master' of https://github.com/plastbox/telldus-core-js
Merge remote-tracking branch 'pb/master'

Conflicts:
	package.json
	readme.md
	telldus.cc
	telldus.js

Resolving merge conflicts