Use precompiled Parse::RecDescent parsers for moar speed

Use precompiled Parse::RecDescent parsers for moar speed

Leverage the (hideous but effective) capability of Parse::RecDescent to
precompile concise gramars into multithousand line monsters. Improves
parsing and thus diffing speed considerably, i.e.:

Testing before:
Files=66, Tests=1851, 23 wallclock secs ( 0.38 usr  0.06 sys + 19.96 cusr  1.80 csys = 22.20 CPU)

Testing after:
Files=66, Tests=1858, 17 wallclock secs ( 0.38 usr  0.08 sys + 15.50 cusr  0.74 csys = 16.70 CPU)

A number of cleanups, including grammar fixes when transitioning from
q{} to heredocs. No functional changes at all.