qd-package.lisp:

o Rearrange some exports so the CMU ones are all grouped together.
o Export new constants pi/2, pi/4, 2pi, and log2.
o Export the qd-real and qd-complex types.

qd-methods.lisp:
o Define new constants for pi/2, pi/4, 2pi, and log2.
o Update some of the macrolets to work with a modern-mode lisp, like
  Allegro.

qd-complex.lisp:
o Use the new constants as needed.