dlist
merge 'undoredo' into 'dlist'

Conflicts:
	src/lib.rs
	src/main.rs
visibility
option -> x, treemap -> hashmap
something
nailed it
i64 -> Revision
fully persistent dlist
visibility
option -> x, treemap -> hashmap
something
nailed it
i64 -> Revision
fully persistent dlist
Merge branch 'dlist' of github.com:zaic/negative into dlist
Travis integration.
Add Travis status image.
i have no idea what i'm doing
Introduce Recall and FullPersistent traits.
Merge branch 'master' of github.com:zaic/negative