Rename Zip::apply to for_each including other apply methods

[bluss]

As mentioned in #858. Use the name Zip::for_each which is more idiomatic than apply.
Users of the azip macro are unaffected.

Renames the following and deprecates the old name:

• apply to for_each
• apply_collect to map_collect
• apply_assign_into to map_assign_into
• par_apply to par_for_each
• par_apply_collect to par_map_collect
• par_apply_assign_into to par_map_assign_into

[SparrowLii]

@bluss The function calls in benches does not seem to be changed. Is there some hindrance?

[bluss]

I just forgot to update those - and then I noticed and forgot again, so it just needs to be fixed to use the new name.