Implement native tmux integration

[junegunn]

Add native --tmux option to replace fzf-tmux script.

Usage

# --tmux [center|top|bottom|left|right][,SIZE[%]][,SIZE[%]]

# Center, 50% width 50% height
fzf --tmux center

# Center, 80% width and height
fzf --tmux 80%

# Center ,100% width and 50% height
fzf --tmux 100%,50%

# Left, 40% width
fzf --tmux left,40%

# Left, 40% width, 90% height
fzf --tmux left,40%,90%

# Top, 40% height
fzf --tmux top,40%

# Top, 90% height, 40% height
fzf --tmux top,90%,40%

Pros

• Simpler and more robust implementation
• Simpler distribution
• Easier to use
• Handles become inside tmux popup better
• Properly propagates environment variables

Cons

• Requires tmux 3.3 or later
• Only opens in a popup which cannot be zoomed