[cdiff] Rename cdiff.sed in preparation for converting to a shell script.
[cdiff] Convert cdiff.sed to cdiff.sh. Execute DIFF if arguments are given.

[mina86@mina86.com: Changed “[ "$*" ]” to “[ $# -ne 0 ]”.]
[cdiff] Move colors to separate configuration.
[cdiff] bugfix: let the last line be colored if needed.

Also, reset colors at the end of any colored line.