update: When rate outside of SoundPool rate range, show a warning message

Signed-off-by: Stephen L. <lrq3000@gmail.com>
update: R.java

Signed-off-by: Stephen L. <lrq3000@gmail.com>
meta-update: README.md and ROADMAP.md

Signed-off-by: Stephen L. <lrq3000@gmail.com>
meta-add: docs

Signed-off-by: Stephen L. <lrq3000@gmail.com>