md5 helper script

This MR adds two helper scripts to compute MD5 checksums for output files in a listening test directory.

The script(s) should be called with a proc_output_X directory as the first positional argument and the desired output file as the second.

# Linux
get_md5.sh /path/to/test/proc_output_X testname.md5

# Windows
get_md5.ps1 \path\to\test\proc_output_X testname.md5

The output produced is now of the format:

file_name.cXX.wav MD5SUMXXXXXXXXXXXXXXXXXXXXXXXXXX

Thanks to @bruhnst and @doehla for the source scripts of the respective versions.