Add special variable for path

There's a {file} variable which is Drive:\Path\to\File\Filename.exe but there's no {path} variable for just the Drive:\Path\to\File part. Because of this, and another limitation (apparent inability to use -o{path} parameter with 7z.exe), I had to make the post-download script change directory to the location of the downloaded file before unzipping it, which required using a for loop to determine the path to the file and set it to a variable. This is a fair bit of extra work, especially considering confusion caused by Ketarin running the commands directly despite making it seem like it's running as a batch file (% vs %%), which would be made much easier by simply being able to say cd /d {path}.