add max-height attribute to ons-pull-hook

[StaymanHou]

Expected behavior

When threshold-height attribute is a negative value, the pull hook should prevent itself from being pulled too far. And developer should be able to specify the max distance (max-height attribute) a user can pull the component

Current behavior

When threshold-height attribute is a negative value, a user can pull the pull-hook component to an indefinite distance which may make the layout look weird.

Proposed solution

The proposed the change adds an max-height attribute to the ons-pull-hook component, by which a developer can specify how far a user can pull it when threshold-height is disabled.

[StaymanHou]

Hi, just wanted to follow up on this PR. Would the change be reviewed and merged? Thanks