Add option to display battery status as hearts in battery.sh

[nikunjmathur08]

#438

This PR restores the "hearts" display for the cute battery mode, as mentioned in issue #438. It also introduces a new symbol option to display the battery status with a battery symbol.

[xx4h]

Thanks a lot for your work!

You're using BATTERY_FULL and BATTERY_EMPTY inside of __generate_hearts() which will just use the battery symbols and not the hearts. I suggest we bring back HEART_FULL and HEART_EMPTY, removed by this commit: cab0747

Besides that, I just have 3 small remarks:

1. Add the missing ;; mentioned by the linter
2. Change TMUX_POWERLINE_SEG_BATTERY_NUM_BATTERIES_DEFAULT to TMUX_POWERLINE_SEG_BATTERY_NUM_HEARTS_DEFAULT in
   

   tmux-powerline/segments/battery.sh

   Line 5 in ba893c9

   TMUX_POWERLINE_SEG_BATTERY_NUM_BATTERIES_DEFAULT=5

   and

   tmux-powerline/segments/battery.sh

   Line 18 in ba893c9

   export TMUX_POWERLINE_SEG_BATTERY_NUM_HEARTS="${TMUX_POWERLINE_SEG_BATTERY_NUM_BATTERIES_DEFAULT}"

   so it matches the other variable and the use case.
3. In

   tmux-powerline/segments/battery.sh

   Line 15 in ba893c9

   # How to display battery remaining. Can be {percentage, cute}.

   add the new hearts option to the doc line?

[nikunjmathur08]

Made the following changes:

• Reintroduced HEART_FULL and HEART_EMPTY variables for displaying hearts.
• Renamed TMUX_POWERLINE_SEG_BATTERY_NUM_BATTERIES_DEFAULT to TMUX_POWERLINE_SEG_BATTERY_NUM_HEARTS_DEFAULT.
• Added the 'hearts' option to the TMUX_POWERLINE_SEG_BATTERY_TYPE documentation.
• Fixed the case statement by adding the missing ;; after the "hearts" case.

Fixes #438

[nikunjmathur08]

I've also removed the extra 7th line.

[xx4h]

LGTM, tested on linux.

Thanks again @nikunjmathur08!

[nikunjmathur08]

@xx4h can you please add this under Hacktoberfest?