Error codes

[panosfol]

I believe we should add error codes by using #define macro. That way we can have uniformity on our return values of our functions.
Each code should be unique and usable by multiple functions and should replace the existing return values i.e:

return -1;

would become

return EFAIL;

or something more specific.
@charmitro thoughts on what are error code naming convention should be?

[charmitro]

Ack and agree.