better Input Method Editor (IME) support

Features:

- Allow input methods swap with hotkey (E.g. left ctrl + left shift).
- Over-the-spot pre-editing style, pre-edit data placed over insertion point.
- Restart IME without segmentation fault.

TODO:

- Automatically pickup IME if st started before IME

win.h

@@ -36,3 +36,4 @@ void xsetmode(int, unsigned int);
 void xsetpointermotion(int);
 void xsetsel(char *);
 int xstartdraw(void);
+void xximspot(int, int);