fix: correctly translate paths when using bash in windows

[nlf]

this fixes the issue when using bash as the script-shell in windows, the problem was that we were passing a windows path to bash as a script to run. to correct it, we translate C: to /c and replace all backslashes with forward slashes. as an example, C:\\Directory\\filename becomes /C/Directory/filename

correcting this problem brought to light a few things that make the module simpler:

1. we no longer need a shebang, or the -c flag when using bash
2. we no longer need to chmod +x the script file
3. we no longer need to escape the filename passed as an argument to bash
4. we no longer spawn a bash that spawns another bash to run your script

no changes were made to the cmd.exe behavior

closes #90