Support in-place scrubbing

[simon04]

Similar to sed. From its man page:

       -i[SUFFIX], --in-place[=SUFFIX]
              edit files in place (makes backup if SUFFIX supplied)

[HEXcube]

Really handy option! :smiley: If implemented, it'll be possible to scour all SVGs in the current folder with a simple command like:

for file in *.svg; do scour "$file" --in-place; done

instead of the nasty workaround I've to use currently :disappointed: :

for file in *.svg; do scour -i "$file" -o "$file"opt; mv -- "$file"opt "$file"; done