Add experimental half precison support

With this MR experimental half-precision support is added

pystencils/backends/cbackend.py

@@ -539,7 +539,9 @@ class CustomSympyPrinter(CCodePrinter):
 
     def _typed_number(self, number, dtype):
         res = self._print(number)
-        if dtype.numpy_dtype == np.float32:
+        if dtype.numpy_dtype == np.float16:
+            return res + '.0f16' if '.' not in res else res + 'f16'
+        elif dtype.numpy_dtype == np.float32:
             return res + '.0f' if '.' not in res else res + 'f'
         elif dtype.numpy_dtype == np.float64:
             return res + '.0' if '.' not in res else res