* color-macros.h: New file.
* diagnostic-color.c: Factor out color related to macros to
color-macros.h.
* doc/gcov.texi: Document -k option.
* gcov.c (INCLUDE_STRING): Include string.h.
(print_usage): Add -k option.
(process_args): Parse it.
(pad_count_string): New function.
(output_line_beginning): Likewise.
(DEFAULT_LINE_START): New macro.
(output_lines): Support color output.