Add GNU "less" style navigation shortcuts to --pager view

[andrewwillowen]

Closes #101 .

Adds the following single-key navigation shortcuts used in GNU less:

Shortcut	Action
f	page down (forward one window)
b	page up (backward one window)
d	half-page down (forward half window)
u	half-page up (backward half window)
g OR 1	jump to first line (1 is a shorthand for the 1+G jump in vi )
G	jump to last line (same in less and in vi)

Since the less navigation does not animate its movements, I chose to do the same with the corresponding actions.
I also neglected to include the e and y one-line movements, since I wasn't sure how to make that happen (and because I didn't know they existed until I looked at the help while writing this PR 😂 ).

I didn't see a contribution.md in the repo, but let me know if there's any reformatting or style changes you would like. I'm happy to make corrections to the PR.

Recommend squash-and-merge if accepted.