The new method uses a table and the taylor series for atan to compute
atan for real args.

qd-const.lisp:
o Add the two tables used for the atan computation.
o Include clisp code that generates the tables.

qd-fun.lisp:
o Implement atan using a set of tables and a Taylor series.

timing.lisp:
o Add a simple timing program to evaluate how fast each atan method
  is.

  OCTI instead of QDI.
o Rename OCT package to NET.COMMON-LISP.OCT, with a nickname of OCT
o Remove nickname of QD.  (Conflicts with other packages dealing with
  quad-doubles.)
o Update all uses of QDI: to OCTI:

qd-fun.lisp:
o Add REM-PI/2 to do a simpler computation if the arg is small
  enough.  Otherwise, use the accurate but expensive rem operation.
o Renamed ACCURATE-SIN-QD to SIN-QD, etc.
o Update SIN-QD etc to use REM-PI/2.