User variables in Build System

[IGRACH]

Add ability to use system variables in Build Systems. I’m using this code for Python build:

Instead of C:/Users/user01, you would use $home, $userprofile, $username, or similar. So if we use portable version of Sublime we do not have to change the path on different machines.

[bschaaf]

"shell_cmd" is a shell command, you can use whatever variables you like for example %HOMEPATH%, %APPDATA% and %LOCALAPPDATA%. You can also add your python installation to your PATH and then you can just run python.exe directly.