v0.3.0

This release starts from adding --height feature, ends up a big change in
the code base.

• feature: --bind accept character keys. Only Ctrl/Alt/F keys were accepted.
• feature: support multiple --bind options. (replace getopts with clap.rs)
• feature: --tac to reverse the order of input lines.
• feature: --preview to show preview of current selected line.
• feature: --height to use only part instead of full of the screen.
• test: use tmux for integration test
• replace ncurses-rs with termion, now skim is fully rust, no C bindings.