internal checkpoint

split kiss_fft.c into multiple files.  It seems the best approach, all things considered.

TIPS

@@ -0,0 +1,16 @@
+Speed:
+    * experiment with compiler flags
+        Special thanks to Oscar Lesta. He suggested some compiler flags 
+        for gcc that make a big difference. They shave 10-15% off
+        execution time on some systems.  Try some combination of:
+                -march=pentiumpro
+                -ffast-math
+                -fomit-frame-pointer
+
+Reducing code size:
+    * remove some of the butterflies. There are currently butterflies optimized for radices
+        2,3,4,5.  It is worth mentioning that you can still use FFT sizes that contain 
+        these factors, they just won't be quite as fast.  You can decide for yourself 
+        whether to keep radix 2 or 4.  If you do some work in this area, let me 
+        know what you find.
+