Difficulty slider and controls improvement

Post-jam update!

Features:

- Added difficulty slider (difficulty affects game speed, stamina decay and presense of extra landing platforms)

- Added volume controls

- Added pause menu

- Ctrl+F4 and Ctrl+F5 will enable/disable all cheats in debug menu

- Collecting cheatcode now plays a sound effect

Changes:

- Walljump controls reworked, should now jump diagonally by default

- Enabled physics interpolation which made the game much smoother on high FPS

- Cloud jump sequence now has a following camera

- Better sound effect for area selection in map level

- Frozen North area will play slow version of theme until you start running section

- You can now exit cloud area from first room

- Under-the-hood code changes

- Debug menu is now bound to letter L

- Improved in-game hints and tutorial

- Doors that lead back to map now hint that they are for leaving

Bugfixes:

- Fixed music looping in web version (hopefully, didn't check)

- Fixed many text alignment issues

- Fixed camera sometimes losing track of player character