Support alternate keyboards

Control keys that weren't bound to actions were ignored to avoid
adding ugly glyphs.  Unfortunately with some keyboard layouts,
important keys like '|' are entered with Control.

Fix is to never ignore control keys and display the actual control
sequence like ^P.  This means some characters can now span more
than one cell.  I haven't done enough work yet to support CJK
characters, hopefully it will be as simple as the couple changes
needed for this fix.
Merge branch 'master' of https://github.com/lzybkr/PSReadLine