fix Num issue.

3.0.2

fix num issue.

fix priority bug.

3.0.1

fix priority issue.

Release 3.0.

only support swift4.

refine anchor chain

3.0.0-beta.3

refine anchor generator.

fix iOS9 issue.

still need refactor some inner impl.

release beta 1.

a big rewrite based on iOS9 Anchors APIs.