Move logic from travis.yml to a Python script

support/build.py

@@ -0,0 +1,13 @@
+#!/usr/bin/env python
+# Build the project on AppVeyor.
+
+from subprocess import check_call
+import os
+
+env = os.environ
+build = env['BUILD']
+if build == 'mingw':
+  # Remove path to Git bin directory from $PATH because it breaks MinGW config.
+  env['PATH'] = env['PATH'].replace(r'C:\Program Files (x86)\Git\bin', '')
+  generator = ['-GMinGW Makefiles']
+check_call(['cmake', '-DFMT_EXTRA_TESTS=ON', '-DCMAKE_BUILD_TYPE=' + env['CONFIG']] + generator, env=env)