This fixes a bug: in the previous version, l_bind_key() modified the
buffer whose address lua_tostring() returned, even though that is not
allowed according to Lua documentation <http://www.lua.org/pil/24.2.2.html>.
The change affects the user interface: previously, if the user typed
"ctrl+cokebottle" in the "Add keybinding" dialog box, ELinks would
change the text in the widget to "Ctrl-cokebottle" before complaining
that the keystroke is invalid. Now, it leaves the widget unchanged.
This commit does not yet add const to parameters of parse_keystroke()
and related functions.
Introduce smjs_init_keybinding_interface, which creates elinks.keymaps.<map>
for <map> in "main", "edit", and "menu". elinks.keymaps.<map> is a hash
indexed by string representations of keystrokes, and can be used to get the
current action for a key and to set the action either to an internal ELinks
action or to an ECMAScript function.
