Add Termux for Android support

[kutsan]

Termux provides very easy API to create and remove notification under Termux on Android. So, it would be very good if you support them.

Related APIs:

• https://github.com/termux/termux-api-package/blob/master/scripts/termux-notification
• https://github.com/termux/termux-api-package/blob/master/scripts/termux-notification-remove

[BlackGlory]

There is also a termux module https://github.com/roccomuso/termux.