Implement PHCpack-based backend for solving polynomial systems.

This extends `enumpoly_solve` with the option to use `PHCpack` [1]_
to solve the systems of polynomial equations.

Closes #165.

.. [1] https://homepages.math.uic.edu/~jan/PHCpack/phcpack.html

ChangeLog

@@ -21,6 +21,9 @@
   of supports to search.
 - `to_arrays` converts a `Game` to a list of `numpy` arrays containing its reduced strategic form.
   (#461)
+- Integrated support (in Python) for using `PHCpack` to solve systems of polynomial equations in
+  `enumpoly_solve` based on an implementation formerly in the `contrib` section of the
+  repository. (#165)
 
 ### Fixed
 - When parsing .nfg files, check that the number of outcomes or payoffs is the expected number,

configure.ac

@@ -145,8 +145,5 @@ AC_SUBST(WX_CXXFLAGS)
 REZFLAGS=`echo $CXXFLAGS $WX_CXXFLAGS | sed 's/-mthreads//g' | sed 's/-g//g' | sed 's/-O. / /g' | sed 's/-I/--include-dir /g'`
 AC_SUBST(REZFLAGS)
 
-AC_CONFIG_FILES([Makefile
-        contrib/Makefile
-        contrib/scripts/Makefile
-	contrib/scripts/enumpoly/Makefile])
+AC_CONFIG_FILES([Makefile])
 AC_OUTPUT