Missing option to control on/off ansi color code ...

Hi,

I have a use case like this:

Use colordiff to view the diff
  
    svn diff | colordiff
    
Apply the patch to another dir (arrow up and edit last command in my shell)

    svn diff | colordiff | patch -p0 -d another-working-copy

Unfortunately this does not work since ansi color chars are piped out to `patch`.  I have to save the diff first:

    svn diff | colordiff > my.patch
    patch -p0 -d another-working-copy < my.patch
    
This is somehow inconvenient, so my fix is to provide a new option `--color=yes|no|auto` similar to grep(1).

Also updated colordiffrc and README.

Thanks,<br>
Matt