flate: add documentation
arena: add docs for Arena
num: expand crate documentation + add example
term: add docs and windows support

Closes #2807
syntax: update for libterm fallout
time: crate description
workcache: add crate doc block
test: update for term fallout
auto merge of #13401 : cmr/rust/docs, r=brson

Adds docs where previously there were no docs. Also adds windows support to libterm.