Big fixes & stability improvements

Notable fix: false-positive error with reschooser no longer happens!

- User input (except URL) is now fully case-insensitive
- Fix invalid batch syntax
- Bump to v2.10.1

Added an important note to intro

Added info when updating run.bat & VARS.txt

Also changed the version number from v2 to v2.1

Update run.bat

Creates a backup of VARS.txt when updating it

Update run.bat

Changed how it works

- Stopped using "set [arg]=[variable]" in favor of "[arg]:[variable]"

Added extra clarification in a comment

Upgraded music downloads

more metadata

Update run.bat