Added a constant for PI which is valid to 20 decimal places.  That seems to be a standard.
Added a constant for PI which is valid to 20 decimal places.  That seems to be a standard.

Whiley/WhileyCompiler,hjwylde/whiley-compiler,hjwylde/whiley-compiler,hjwylde/whiley-compiler,hjwylde/whiley-compiler,hjwylde/whiley-compiler