Mathomatic 15.4.3

Added compile.mingw to easily compile Mathomatic for Windows 32-bit using the
MinGW cross-compiler (Ubuntu package gcc-mingw32) and attach icons/mathomatic.ico
to the generated mathomatic.exe file.

1/29/11 - Easily allow groff instead of rman in makefile for creating web pages
          out of the man pages. Some distros don't have rman.

2/02/11 - Fixed negate priority to be the same as TIMES/DIVIDE like Maxima (yay!).
          So now entering -x^2 is meaningful. Previously negate was the highest
          priority (high precedence) operator. Entering -2^2 now results in -4
          instead of 4, as in most other mathematics programs (except for pure
          calculators like bc).

2/04/11 - Flush standard output before reading a line of input from the user
          when not using readline, so that the MinGW version works with mintty.

2/06/11 - Added a new "for" command, for plugging in sequential values into a
          variable in the current expression and displaying the results.
          The syntax is the same as the sum and product commands.