Map multiple key sequences to the same callback

[clarity20]

Description

Can we add a "many-to-one" behavior to the key mappings, so for instance if my .vimrc says

    let g:NERDTreeMapHelp = ['<F1>', '?', 'h']

I would have 3 ways to open the help menu?

And in the help menu itself we would see

    " <F1>|?|h : toggle help

Thank you!