treemap: rm a bit of redundant code
update comments documenting issue #4492 workaround
add is_subset and is_superset to the Set trait
add is_disjoint to the Set trait
Add Felix Klock to AUTHORS
add difference and symmetric_difference to Set
add intersection and union to the Set trait
De-capitalize "note" to get rid of spurious tidy warnings
rustdoc: Remove structural records from tests. Fixes build breakage
std: Stop using oldcomm
Merge pull request #4682 from thestinger/treemap

Set trait improvements + minor treemap cleanup
core: convert ToStr::to_str to take explicit &self