Clarify meaning of $&

[sogaiu]

This PR is a suggestion to clarify the meaning of $& as currently expressed on the function page:

Similarly, $0, $1, etc. refer to the arguments at index 0, 1,
etc. and $& refers to all passed arguments as a tuple.

IIUC, when $, $0, ..., $i is/are used, $& refers to less than "all passed arguments":

(|[$0 $1 $&] 1 0 -1)
# =>
[1 0 [-1]]

(|[$ $&] 1 0)
# =>
[1 [0]]

The suggested change is to express the above as:

Similarly, $0, $1, etc. refer to the arguments at index 0, 1,
etc. and $& refers to all remaining arguments as a tuple.

i.e. saying "all remaining arguments" instead of "all passed arguments".

[pepe]

LGTM