Fix `bind -e` without `-k`

In adding `-k` support to `bind -e` I broke the ability to use `bind -e`
without specifyign `-k`. Oops.
Rework mode handling of `bind`

Binds with the same sequence in multiple modes was not working right.
Fix up the implementation to propagate modes everywhere as necessary.
This means that `bind` will properly list distinct binds with the same
sequence, and `bind -e` will take mode into account properly as well.
Note that `bind -e seq` now assumes the bind is in the default bind
mode, whereas before it would erase the first binding with that sequence
regardless of mode.

`bind -e -a` still erases all binds in all modes, though `bind -M mode
-e -a` still only erases all binds in the selected mode.
Fix build failure

std::vector::erase() didn't take const_iterator until C++11 >_<
Support `bind SEQ` to print a binding for `SEQ`
Suppress italics in keyboard shortcuts
lexicon_filter fix for escaped options

Fixes #1703. Also fixes short and long options markup in synopsis when
directly following a '(' or '[' character.
Restore DejaVu Sans Condensed font.

With font-strentch: condensed, the rendering is acceptable.