Allow importing as a module. Added prefix argument to allow building …

[superr]

…prefix.new.dat. Added argument parsing when run as a script to allow mixing options. Fixed directories not being created when outdir argument is provided causing a crash.

Usage as a script is different, and the README has been updated:

./img2sdat vendor.img -o tmp -v 4 -p vendor

The default prefix is "system" if -p is not used.

Usage as a module:

import img2sdat

img2sdat.main(INPUT_IMAGE, OUTDIR='.', VERSION=None, PREFIX='system')

Looks like this also fixes issue #12 and #13 :)

[superr]

Sorry for closing it. I thought I missed something but the error was in my command, not the tool :)

[xpirt]

Looks good.

Merged.