Do all input through one ReadLine() routine

Do all input through one ReadLine() routine

Some duplicate code now is made into a subroutine, to which we pass
the stream from which it should read a line, and the buffer to hold
the result. It returns whether the read was succesful (i.e. no EOF).
As this can also easily fake engine output from a file, the special
routine GetChar()we had for this could be abolished.