Refactor android-builder into command scripts

lib/commands/doctor.sh

@@ -0,0 +1,19 @@
+#!/data/data/com.termux/files/usr/bin/bash
+set -e
+
+ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
+source "$ROOT_DIR/lib/common.sh"
+
+echo "AndroidBuilder Doctor"
+echo
+
+java -version
+echo
+gradle -v | grep Gradle
+echo
+aapt2 version
+echo
+
+test -f "$SDK/platforms/$PLATFORM/android.jar" \
+  && echo "android.jar: found" \
+  || echo "android.jar: missing"