Generate md5 files for each folder while copying

Since Teracopy is already calculating the md5 hash for the verification it should be quite easy to write them in a .md5 file for each folder. This should of course be optional.

As extension of this, it would also be possible to double check the source file against such an .md5 file so that you can immediately see if the source was changed (which can be ok for e.g. office documents and will not be ok for e.g. pictures or movies).