Pyxel

- Fixed the bug where Pyxel Editor cursor malfunctions
- Added new API descriptions to Example 3
- Updated the screenshot of Example 3
- Change to not add unnecessary undo history of the editors
- Added the setting files for Pipenv
- Modified the cursor design of the image/tilemap editor
- Enabled to change the focus size of the tilemap editor
- Added the link to the subreddit in the manuals
- Changed to exports all constants for keys before init is called
- Added the contribution section to the manuals

- Fixed the tilemap to allow the tiles of 256 or higher
- Updated the screenshots of Pyxel Editor
- Fixed the cursor movement of the sound/music editor
- Changed the caption of Example 2
- Renamed Example 6
- Fixed the error when saving long animated GIF

- Added the .pyxel file to the install example script

- Fixed the piano keyboard bug when only enter was pressed
- Fixed the piano keyboard highlights correctly
- Changed the default sound volume to 7
- Changed the default sound speed to 30
- Fixed the sound button bug of the sound editor

- Changed the operation method of the sound editor
- Changed to allow sound of length 0
- Implemented the music editor
- Changed Example 2 to use resource file

- Implemented the undo function of the sound editor
- Changed the click tolerance time
- Removed the length limitation of the sound
- Added the music and playm APIs
- Changed Example 2 to use the music and playm APIs