* feat: define dark and light color palettes
* feat: add customization of status-right & status-left sections
* feat: rename to gruvbox_dark256 and implement alpha option
* fix: transparency for tabs in left status bar
* fix: shellcheck errors
* fix: files according to shfmt
* feat: remove unnecessary modeline
* feat: save palettes as 256 color
* feat: update information about dark256 & light256 themes
* chore: add changelog entry
