Return error message when OpenCL operations fail

[avramidis]

Is your feature request related to a problem? Please describe.
The problem is that when calling an OpenCL operation there isn't a clear error message that the operation failed.

Describe the solution you'd like
The function that implement the OpenCL operations must return an error message that can be used by the other parts of SODECL. Moreover, it have to give proper information to the user about what went wrong. It would be best each function that implement OpenCL operations to throw a custom exception for the specific OpenCL error.

Describe alternatives you've considered
The ways that an error can be returned from functions is by exceptions, return value or change of value of an argument.