Support for custom Seed projects

[grrrwaaa]

May require some larger changes to genlib_daisy.h, a custom target JSON, etc.

Also documentation of how to do it!

[grrrwaaa]

• Oopsy.js can already handle paths to JSON files as target definitions in the arguments.
• "special case" code in genlib_daisy.h needs to be filtered out as much as possible and turned into properties of target JSON files. This is partially done.
• Config files will need extra sections to insert necessary code into the main() for configuration of pins etc., processAllControls equivalent for the audioCallback, anything similar into the main or display callbacks, etc. There is now an "inserts" array in the JSON with "where" ("header"/"init"/"main"/"display"/"audio") and "code" sections as a general way of doing this.
• Max interface needs a "browse" button to search for a custom interface definition JSON and pass that through to oopsy.js; and a @target option to make that default?
• Documentation needed for the requirements and options of the JSON files.

[grrrwaaa]

Max interface now updated in dev branch to include browse and @target support for custom JSON configs. Support for insert code sections has now been added to the code generator and JSON schema.

This may be ready for alpha testing to identify any missing capabilities. Documentation still required.

[grrrwaaa]

Created wiki page to document this here: https://github.com/electro-smith/oopsy/wiki/Custom-Seed-Targets

[grrrwaaa]

release/tag v0.4.0 introduces a new JSON format:

https://github.com/electro-smith/oopsy/wiki/Custom-Seed-Targets

This remains a work in progress, but has been designed in coordination with @stephenhensley to make it simple to create a quick template for breadboarding type projects. As of now it does not handle OLED, SDcard, I2C, UART or anything like that, mostly just GPIO stuff.

The old JSON formata also continues to function in the meantime.