Ignore all control characters not handled

Ignore all control characters not handled

Taken from vt100 programmer manual:

	Control characters have values of \000 - \037, and \177. The control
	characters recognized by the VT100 are shown in Table 3-10. All
	other control codes cause no action to be taken.

We have to take attention when we are using alternate charset, because in
this cases they are not used as control characters.
---
 st.c |   20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)