Changed the way keys are processed.

Until today vimb mapped two-part keybindings to commands. This patch changed
this paradigm into a more vi like way. The commands are separated into normal
mode commands that mainly consists of a single char and ex commands that can
by typed into the inputbox like ':open'. This change allows us to adapt also
the way keypresses and mapping are handled. Now every keypress is converted
into a unsigned char and collected into a typeahead queue. The mappings are
applied on the queue. So now we can use also long keymaps and run multiple
commands for different modes with them like ':nmap abcdef :set
scripts!<CR>:open search query<CR>50G'.
Allow to bind also function keys.
Allow to run multiple ex commands.

Ex commands can be joined with | like following example:

    :set scripts!|set plugins!

Or bound to a key sequence:

    :nmap <C-F1> :set scripts<CR>:set plugins!<CR>:open !tag<Tab>
Cleaned the code a little.

Remove already solved tasks and changed most of the *var == '\0' into !*var
expressions.
Removed all default webkit settings from default.h.

This makes the startup a little faster. By they way, a typo in a configuration
was fixed.
Added cursor to default key bindings.

Removed those cursor keybindings that where introduced to fix an issue that
does not exist anymore.
Show the last keys of keysequence in statusbar.
Adapted manual page to the new key handling.
Adapted the README file.
Added missed normal commands 'O' and 'T'.
Leave input mode if a form submit loads a page.

Also remove the old vb_set_mode function that become obsolete.
If possible use g_strconcat instead of g_strdup_printf.
Removed string length restriction of vb_echo functions.
Set mode according to current focused widget.
Removed announcement about changed history file format.
Fixed wrong mapped 'T' and 'O' commands.
Removed g commands from map.

Is is easier to call the g commands like the other commands that needs
multiple chars instead of setting the 8th bit of the char.
Don't allow to paste multline content from clipboard.

If the pasted contents leads to multiple input box lines, we remove everything
out of the buffer except of the first line.
Remove no more used enum and macros.
Removed nor more used count.