Introduce the CORDIC algorithm.
o sine and cosine (e.g., FSIN, FCOS and FSINCOS instructions) is now
  calculated in the CORDIC instead of Taylor expansion.
o tangent (FTAN) is not touched from a viewpoint of the code size.
o The CORDIC is applicable for hyperbolic functions (e.g., FSINH,
  FCOSH, FTANH instructions), but I didn't use it because its working
  range is poor.
o The CORDIC is also usable for inverse trigonometric functions,
  I will commit it at next phase.
o The code size becomes a bit big.  I cannot evaluate speed on m68k
  for some reasons, but in test on i386 the CORDIC is approximately
  100 times faster in sin/cos.

(isaki)