add support of indicator start and end

[aacebedo]

I have added the support of characters at the start and the end of the indicator.
It is backward compatible with current behaviour and allow to create nice pill like indicator like this:

[MunifTanjim]

This plugin is intentionally kept simple. (ref:

tmux-mode-indicator/README.md

Line 17 in 7027903

_Note: This is a trimmed down version of the original [tmux-prefix-highlight](https://github.com/tmux-plugins/tmux-prefix-highlight) plugin._

)

What you want can be done like this:

mode_separator_style="#[default]#{?client_prefix,#[fg=blue],#{?pane_in_mode,#[fg=yellow],#{?pane_synchronized,#[fg=brightred],#[fg=cyan]}}}"
mode_separator_start="${mode_separator_style}${mode_separator_style}#[reverse]"
mode_separator_end="${mode_separator_style}${mode_separator_style}#[default]"

set -g @mode_indicator_prefix_prompt "${mode_separator_start}WAIT${mode_separator_end}"
set -g @mode_indicator_prefix_mode_style ""
set -g @mode_indicator_copy_prompt "${mode_separator_start}COPY${mode_separator_end}"
set -g @mode_indicator_copy_mode_style ""
set -g @mode_indicator_sync_prompt "${mode_separator_start}SYNC${mode_separator_end}"
set -g @mode_indicator_sync_mode_style ""
set -g @mode_indicator_empty_prompt "${mode_separator_start}TMUX${mode_separator_end}"
set -g @mode_indicator_empty_mode_style ""

set -g @plugin 'MunifTanjim/tmux-mode-indicator'