allow additional includes to be specified in the parse config

[stijnveenman]

implements part of #101
This PR adds support for additional includes to be passed to the preprocessor.
This in turn adds support for zmk-helpers as its path can be added to the parser config as follows

parse_config:
    zmk_additional_includes:
      - "zmk-helpers/include"

While this does not parse the west.yaml, i think it should be sufficient for most, if not all, use cases. As most configurations will not have many additional includes.

To fully implement #101 the workflow also has to be updated to pull west modules. I plan on picking this up seperately

[caksoylar]

Thanks for the PR! It looks pretty good on an initial glance, I'll properly review it when I am home next week.

[stijnveenman]

Quickly fixed formatting and linting. Not sure what a straightforward way to fix the too many arguments warning is.
As during the constructor of DeviceTree we need the additional includes to call _preprocess. Otherwise we would have to pass the entire config object. Happy to change this if you have any preference

[caksoylar]

Don't worry about that one, I usually add a disable comment if it will be too inconvenient to obey it.

[caksoylar]

Looks pretty much perfect, thanks again.