Squashed 'External/Lagrangian/' content from commit 0b819d4

git-subtree-dir: External/Lagrangian
git-subtree-split: 0b819d48949280b7320cd8d6852a6f0e0d7f5a88
Adds Lagrangian to the project as a subtree.

Merge commit '75d73fc44ac4e8ea176b1b59f28e56c68009c962' as 'External/Lagrangian'
Adds Lagrangian to the project.