Create "-ing" aliases for iteration commands

[okamsn]

Many iteration commands have aliases taken from cl-loop, such as in for
list from for VAR in LIST. In loopy-iter, this gives up for in VAR LIST
instead of for list VAR LIST. When lax-naming is enabled, we get in VAR LIST.

For me, this has never been satisfactory. It would be better to have forms like
listing and arraying, which, besides being more in line with alias like
unioning and appending and so easier to remember, is clearer when using
lax-naming.

This gives us two clear forms: (for list VAR LIST) and (listing VAR LIST),
depending on whether lax-naming is enabled.

The prepositional aliases can remain, but they should no longer be featured
prominently.

[okamsn]

These aliases have been added.