Add support for custom key bindings

[fujiapple852]

Adds the --tui-key-bindings and --print-tui-binding-commands command line options.

Use --tui-key-bindings as follows:

trip --tui-key-bindings previous-hop=k,next-hop=j,quit=shift-d

The above will bind the key k and j to the previous-hop and next-hop commands respectively and binds the key shift-d to the quit command.

The supported modifiers are: shift, ctrl, alt, super, hyper & meta.

Multiple modifiers may be specified, for example ctrl-shift-b.

Use --print-tui-binding-commands to print out all available commands that can be bound. Currently these are:

Command	Description	Default
toggle-help	Toggle help	h
next-hop	Select next hop	down
previous-hop	Select previous hop	up
next-trace	Select next trace	right
previous-trace	Select previous trace	left
address-mode-ip	Show IP address only	i
address-mode-host	Show hostname only	n
address-mode-both	Show both IP address and hostname	b
toggle-freeze	Toggle freezing the display	f
toggle-chart	Toggle the chart	c
expand-hosts	Expand the hosts shown per hop	]
expand-hosts-max	Expand the hosts shown per hop to the maximum	}
contract-hosts	Contract the hosts shown per hop	[
contract-hosts-min	Contract the hosts shown per hop to the minimum	{
chart-zoom-in	Zoom in the chart	=
chart-zoom-out	Zoom out the chart	-
clear-trace-data	Clear all trace data	ctrl-r
clear-dns-cache	Flash the DNS cache	ctrl-k
clear-selection	Clear the current selection	esc
toggle-as-info	Toggle AS info display	z
quit	Quit the application	q