Add a find method

The find method is a flexible find that produces the first non
undef value produced by a block called for each element in an
iteration. Produces undef if no non-undef value was produced or
if the enumeration was empty.

Like all other iterative functions the block can be specified
with one or two parameters to get key/index, and value, or just the
value.
Fix typos in docs for any and all