Reduce subshells created by percent·encoding

It’s possible to use `%0A` as a component separator assuming that
file·names will never contain newlines; this allows all filenames to
be processed at once rather than needing a separate subshell for each.

It’s not necessary to encode each path component separately; just
encode the whole path and replace `%2F` with `/` at the end. It’s not
possible for file·names to contain literal `/` characters.

The above two changes should increase the speed of operations such as
building the parser catalog in ⛩️📰 书社 considerably.