Add Stackless 2.7.16 (#1450)

* Added Stackless 2.7.16

Co-authored-by: Nathan <nathan@nathan.v>
Co-authored-by: Ivan Pozdeev <vano@mail.mipt.ru>

plugins/python-build/share/python-build/stackless-2.7.16

@@ -0,0 +1,4 @@
+#require_gcc
+install_package "openssl-1.0.2k" "https://www.openssl.org/source/openssl-1.0.2k.tar.gz#6b3977c61f2aedf0f96367dcfb5c6e578cf37e7b8d913b4ecb6643c3cb88d8c0" mac_openssl --if has_broken_mac_openssl
+install_package "readline-8.0" "https://ftpmirror.gnu.org/readline/readline-8.0.tar.gz#e339f51971478d369f8a053a330a190781acb9864cf4c541060f12078948e461" mac_readline --if has_broken_mac_readline
+install_package "stackless-dev-stackless-43302de87df4" "http://www.stackless.com/binaries/stackless-2716-export.tar.xz#2db64fbd47567a1c0683fba7a54387892d2299915f9848b54c450b5eb95358dc" standard verify_py27 ensurepip