feat: add shellcheck & shfmt github actions (#33)

* refactor: separate lint shfmt and shellcheck
* feat: add simple github action task
* fix: linting bash files according to shfmt
* feat: move main method dedicated shell file
* feat: update changelog entry

src/gruvbox-main.sh

@@ -0,0 +1,27 @@
+#!/bin/bash
+
+SCRIPT_SRC="$(dirname "${BASH_SOURCE[${#BASH_SOURCE[@]} - 1]}")"
+readonly SCRIPT_SRC
+CURRENT_DIR=$(cd "${SCRIPT_SRC}" >/dev/null 2>&1 && pwd) readonly CURRENT_DIR
+readonly THEME_OPTION="@tmux-gruvbox"
+readonly DEFAULT_THEME="dark"
+
+get_theme() {
+  local option="$1"
+  local default_value="$2"
+  local option_value
+  option_value=$(tmux show-option -gqv "$option")
+  if [ -z "$option_value" ]; then
+    echo "$default_value"
+  else
+    echo "$option_value"
+  fi
+}
+
+main() {
+  local theme
+  theme=$(get_theme "$THEME_OPTION" "$DEFAULT_THEME")
+  tmux source-file "$CURRENT_DIR/tmux-gruvbox-${theme}.conf"
+}
+
+main "$@"