vloader and switchconv: simple mods for Linux and Switch

[leo60228]

vloader: Add libvloader.so to your LD_PRELOAD when launching VVVVVV on Linux for the following additions:

• Skip the fake loading screen entirely (including the flashes at the end, unlike the hexedit)
• Allow symlinks in ~/.local/share/VVVVVV (or $XDG_DATA_HOME)
• If a number is specified as an argument to the game, launch the custom level with that index in the menu (starting from 0) immediately. Note that the wrapper shell script doesn't pass-through arguments, so you'll need to either modify it or launch vvvvvv.x86_64 directly.

switchconv: Run this Python 3.8+ script from a level folder (your working directory should contain a levels folder, not .vvvvvv files directly!) to convert the level to a LayeredFS mod. Levels, sprites.png, and vvvvvvvmusic.vvv will be converted to work on the Switch, and other files (most of which will work without modifications) will be copied.