[varLib.iup] Compile with Cython when available

Even with no annotations, makes it ~35% faster.

Lib/fontTools/varLib/iup.py

@@ -1,3 +1,17 @@
+try:
+	import cython
+except ImportError:
+	# if cython not installed, use mock module with no-op decorators and types
+	from fontTools.misc import cython
+
+if cython.compiled:
+	# Yep, I'm compiled.
+	COMPILED = True
+else:
+	# Just a lowly interpreted script.
+	COMPILED = False
+
+
 MAX_LOOKBACK = 8
 
 def iup_segment(coords, rc1, rd1, rc2, rd2):

setup.py

@@ -68,6 +68,9 @@ if with_cython is True or (with_cython is None and has_cython):
 	ext_modules.append(
 		Extension("fontTools.cu2qu.cu2qu", ["Lib/fontTools/cu2qu/cu2qu.py"]),
 	)
+	ext_modules.append(
+		Extension("fontTools.varLib.iup", ["Lib/fontTools/varLib/iup.py"]),
+	)
 
 extras_require = {
 	# for fontTools.ufoLib: to read/write UFO fonts