add transparency on start

[yazgoo]

Create options (disabled by default) to allow "transparency" in tuikit. more precisely: retain cells which don't need to be changed as they were before tuikit was started.

example

With win example with the new options:

                TermOptions::default()
                    .disable_alternate_screen(true)
                    .clear_on_start(false)

Running in shell:

clear
# display an image in term:
blockish /home/yazgoo/Pictures/vimpapers/73lfih7qkrr61.png 
# move cursor to top left:
echo "\e[0;0f"
# run pre-compiled win example:
./target/debug/examples/win

Results in:

new options

• clear on start (default: true): when set to false, will never erase to end of line or erase down
• disable alternate screen (default: false): when set to true, never run rmcup/smcup

[yazgoo]

UP ?