Add self-update command to refresh miaur from Git

Introduce `miaur self-update` / `--self-update` that clones RepoUrl@Branch,
detects user vs system install prefix, and reinstalls in place. Configurable
via conf/env; supports --noconfirm, --repo-url, and --branch.

Co-authored-by: Frank Vitrano <WHC2006@users.noreply.github.com>

lib/common.sh

@@ -2,7 +2,7 @@
 # shellcheck disable=SC2034
 # Common utilities for miaur
 
-MIAUR_VERSION="0.1.0"
+MIAUR_VERSION="0.2.0"
 
 # Colors (respect pacman Color / NO_COLOR / non-tty)
 _miaur_color_enabled() {