rewrite readme overview using defending base example
Revert "rewrite readme overview using defending base example"

This reverts commit 51d111995a779a348cc97d1be7367a80095feb7a because the new overview was long and didn't necessarily explain things better.
Fix memory leak.
rename Tile.coherence to exclusive, Unit.timeCohere to timeUnseen
Merge branch 'master' into stacking
fix compile error after merge
apply Unit method renames to Path class
add back nonzero tight formation spacing