migrates to paradise 2.0.0-M2

It all went smooth apart from the necessity to upgrade to 2.10.3,
because I currently don't have milestone releases published for 2.10.2,
only 2.10.3 and 2.11.0-M7 (but I can fix that if necessary).

The two minor changes were necessary, because the implementation of
quasiquotes has evolved to be a bit more picky.
in 2.10.x parallelExecution of reflection-based tests is dangerous

Runtime reflection is thread-unsafe in 2.10.x, therefore running `sbt test`
was giving me a bunch of spurious failures.