Very good job, thanks Jantje!!!
Just a point that could be better:
Each boards.txt entry has an "build.core" field, for example for uno:
uno.build.core=arduino
This allows to add alernative cores (as i do), then it could be great that this plugin takes this in account instead of always use the "arduino" core.
A cuestion:
Do you have highlighting for arduino functions ( for example delay() )??
In other projects sometimes i have it and sometimes i haven't... the indexer looks to work ramdomly well/bad.
Best regards.