Squashed 'External/Lagrangian/' changes from 1bb3228..c3f5d01

c3f5d01 Merge pull request #14 from robrix/develop
b56a2ba Merge pull request #12 from robrix/feature/concision
d18cc71 Break the circular dependency.
a4217f5 No more janky double imports.
17ee93c No more mocks.
40e20f1 Replace RXPreprocessing with metamacros.h.

git-subtree-dir: External/Lagrangian
git-subtree-split: c3f5d01c26792a4673eab56554948916626dd9dc
Merge commit '3d433374f616d7fd03efa37f0239f151ceb3eed2'