added boolean accessors (eg: isVisible instead of getVisible), client error is returned, not thrown.

[ruxkor]

I added several improvements to the existing soda library, namely the

• correction of all boolean accessors: several commands are not callbable via get*, such as visible. They have to be called with "is". This is corrected in my version.
  • the soda client uses an eventemitter (the standard http client), but implements a callback pattern. since the original client is hidden, it is impossible to catch any soda client error on application level. in order to access the error, I simply call the callback function with the error as first value.
  • docs are updated of course

[ruxkor]

closing this as it was never tackled.