Add notes about semantics of 'select' and 'o concentric'.
Add FormationMatch.inserted to track phantom dancers.

When evaluating "triple lines" or other formations which insert phantoms,
we need to keep track of which phantoms we've added so that we can remove
them again after the call is evaluated in the formation.  There may be
multiple nested concepts which each add their own phantoms, so we can't
just remove all NONCORPOREAL dancers, we need to be specific about which
formation match added which.
Add "use phantoms" matcher.
EvalPrim.apply() can now dance with phantoms.

We can't always apply a Prim to a dancer with an inexact rotation, but
if the direction is to stand still or is given using in/out/roll/sweep
modifiers we often can.

Dancer paths can now have inexact facing directions; thankfully these
paths are removed before we actually have to animate them.