chore(reorganize): reorganize project files

[mellodev]

Description

The goal of this PR is to clean up the project folder/file structure a bit to improve readability and maintainability. Moving the source files, header files and scripts out into dedicated folders seems like a good first step. This means lots of changes/refactors were made to #include statements, bash scripts and the github workflow yml. Lots of opportunity to accidentally break things here, so please review carefully!

This PR:

• Moves all .cpp/.c files to /src
• Refactors build.sh g++ commands to pull in all files from /src rather than a hardcoded list
• Moves all .h/.hpp files to /include
• Refactors all #include statements to use new paths
• Moves all bash script files to /scripts
• Refactors various files which invoke scripts to use new path
• Updates SOURCES and HEADERS paths in Makefile

Things that don't seem right

⚠️ build.sh demo does not successfully compile on my end (but VSCode/Pio does). Could be environment specific, but please verify:

⚠️ build.sh g++ commands might need a little path tweaking for src and output folders
⚠️ make all also fails for me due to a WProgram.h missing include. Likely another environment specific issue?
⚠️ There were two changes made for #include statements for WProgram.h and Arduino.h. These can probably be reverted as they didn't resolve the build.sh demo failure I am having. VSCode/PlatformIO builds the project correctly either way.