Tiny-slider: Arrow Keys still work while option is disabled and focus is on .tns-controls

[afberg]

__Issue description__: The arrow keys still work while focus is on the .tns-controls element, visible in the demo pages.

Furthermore the up/down arrow keys change the slides in horizontal sliders and they also scroll the screen up/down which seems like very confusing behaviour.

__Demo link/slider setting__: http://ganlanyuan.github.io/tiny-slider/tests/index.html

_Tiny-slider version_: 2.8.6
_Browser name && version_: Chrome v69.0.3497.92
_OS name && version_: macOS High Sierra Version 10.13.6

[ganlanyuan]

The arrow keys still work while focus is on the .tns-controls element, visible in the demo pages.

This is for accessibility and is expected.

Furthermore the up/down arrow keys change the slides in horizontal sliders and they also scroll the screen up/down which seems like very confusing behaviour.

I will add an additional key to prevent the scrolling of page.

[afberg]

This is for accessibility and is expected.

Since it is for accessibility an update to the readme would be nice to avoid future confusion :)

[ganlanyuan]

Readme updated

[ganlanyuan]

Furthermore the up/down arrow keys change the slides in horizontal sliders and they also scroll the screen up/down which seems like very confusing behaviour.

This is fixed in this commit.
These keys are removed: up, down, pageup, pagedown, home, end.