move python demos to _pydemo

_pydemo/callpy/call.go

@@ -0,0 +1,16 @@
+package main
+
+import (
+	"github.com/goplus/llgo/c"
+	"github.com/goplus/llgo/py"
+)
+
+func main() {
+	py.Initialize()
+	py.SetProgramName(*c.Argv)
+	math := py.ImportModule(c.Str("math"))
+	sqrt := math.GetAttrString(c.Str("sqrt"))
+	sqrt2 := sqrt.CallOneArg(py.Float(2)).FloatAsDouble()
+	c.Printf(c.Str("sqrt(2) = %f\n"), sqrt2)
+	py.Finalize()
+}