Merge pull request #6 from Thus0/Thus0-patch-compile-on-windows-msys2

patch to compile tinydtls on Windows (MSYS2) : autoconf is found during compilation 

setup.py

@@ -17,9 +17,9 @@ class prepare_tinydtls(build_ext):
                 sys.exit(1)
 
         commands =  [
-                    ["autoconf"],
-                    ["autoheader"],
-                    ["./configure", "--without-ecc"],
+                    ["sh", "-c", "autoconf"],
+                    ["sh", "-c", "autoheader"],
+                    ["sh", "-c", "./configure", "--without-ecc"],
                     ]
         if not os.path.exists(os.path.join(os.path.dirname(__file__), 'DTLSSocket','tinydtls','dtls.c')):
             run_command(["git", "submodule", "update", "--init"])