Add line number and colum number to all warnings/errors/debug messages.

It would be nice enhance the callback_function to have the line number/col number where an issue was raised.

This might mean improving internal_parse( ... ) so that source is a class that helps us keep track of where we are.

NB: In some cases there is no line number and so on, (for example when we are looking for a key/value pair or file open error, in cases like that I guess we can pass -1 as line number.