Expected pager behaviour in `Help` closes the overlay about hired

[sidju]

Taking some notes here in prep for when I actually get to coding on this next.
If anyone else has the time and energy feel free to make a PR of this change, otherwise it is likely to not be added until summer.

Input handling code for the Help and help overlay:
https://github.com/sidju/hired/blob/master/src/hui/doc_print.rs#L49

Commands to add (inspired by man pages for less and more):

• u, scroll up (by half a screen height in less, 11 lines in more)
• d, scroll down (by the same amount as u)
• s, alias to enter
• b, alias to page up
• f and z, alias to page down
• r, R or ctrl+L, noop without closing help (aka. redraw)
• g or home, go to line 1
• G or end, go to last line