Merge pull request godotengine#453 from aaronfranke/plugin-proj

Refactor the plugin demos to be inside of a project and add main screen plugin demo

Merge pull request godotengine#407 from aaronfranke/3.1

Remove BPM Sync demo from the 3.1 branch

Merge pull request godotengine#348 from texaco/master

Fix seesaw falling plank from 2d demo

Merge pull request godotengine#205 from vnen/fix-reverb-platformer

Fix reverb predelay feedback for platformer 3d

Merge pull request godotengine#108 from TwistedTwigleg/Particles_2D_r…

…edux

Redid the particles 2D demo

Add gitignore

Allow changing player facing side while in the air

* As soon as the user wants to change direction while in the air, change
  the character's facing side.
* This allows for example shooting left then right while in the air and
  gives a better feeling.

Adapted from @stormi's 8ff2aec.

Added Input.set_mouse_mode(...) test cases.

(cherry picked from commit ee75abe)

free coin in 3D platformer

(cherry picked from commit 76bfb10)