Add TBC sequence

Add TBC sequence
This sequence clears tab stops in the terminal. If the argument is not present
or is zero, then removes the tab stop of the current horizontal position. If
the argument is 3 then removes all the tab stops of the terminal. It was
necessary modify the terminfo entry tbc, because it has \E[2g instead of the
correct \E[3g.

Signed-off-by: Roberto E. Vargas Caballero <k0ga@shike2.com>
---
 st.c    |   12 ++++++++++++
 st.info |    2 +-
 2 files changed, 13 insertions(+), 1 deletion(-)