Faster tree generation

[MarcellPerger1]

• [x] Implement faster (in theory) tree generation
• [x] Test the speed compared to other algorithm
• [x] Use that data to switch between implementations
• [x] Config to manually chose implementation

Fixes #119.

[MarcellPerger1]

The new implementation seems to be faster in all cases, for tests see 4ec2b76cdb2a7cbd98d0f26f2e3556a8772f67cc

[MarcellPerger1]

• [x] TODO: move those tests to a sensibly-named directory