Add custom handling of up, down, PgUp and PgDown

[KennethAshley]

Why?

#46

What changed?

• Added keybindings for up, down, pageup and pagedown.
• Also added e.preventDefault() so content doesn't jump

Example

Although you cannot tell i am pressing up, down, page up and page down.

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[x1ddos]

Sorry but we can't merge without CLA.

[x1ddos]

I don't believe this actually solves #46 at all.
Let me know if you disagree.

[x1ddos]

This is the opposite of #29, which was done for a specific and clear reason.
Not sure what re-adding it here solves vertical scrolling issue described in #46.

[x1ddos]

Closing due to unclear intent in the change, missing CLA and no activity.