Modified Scribble indentation functions to support "line push back"(combine concurrent short lines)

If current line under indentation is shorter than the user defined maximum line width, we keep pushing back lines after it until:
(1) we see an @ sign as the first non tab/whitespace character of the line after current line
(2) we see an empty line
(3) we exceed the last line of the source code file(end of file)
(4) current line became longer than user defined maximum line width(after a sequence of “push-back”), then apply the adjust-para-width function to it