Merge branch 'master' of github.com:zaic/negative.
Revert some changes.

Conflicts:
	src/dlist.rs
	src/inner/kuchevo.rs
	src/inner/persistent.rs
	src/inner/versioned_fat_node.rs
	src/map/pers_map.rs
	src/vector/pers_vector.rs
Fix.
fixed lifetimes
custom reference type for use in mutable iterators,
also moved revision history to revision tree and implemented mutable iterator for dlist
set proper head in iter_mut
update head only if necessary
i have nothing to say