Change source and sink methods so, that they use the Result type as a return value for most methods.

[dankwart-de]

Why? Because in the current implementation, the methods like readChar, read or write are very C/C++'ish and return e.g. -1, if "bad things happen". With the Return type, we can have a modern approach which
a) returns success or not
b) returns a result, if successful
c) can hold a message, describing the nature of the error.