Reformat some code

Avoid using ViewCompat.isLaidOut() that does not check the view attach state for APIs < 19.

Update the files' execute permission

Ensure pending runnable to run at the expected time when layout is valid.

Update README.md

Add release notes

Bump version to 2.1

Upgrade some dependency versions

Add overscroll effect for each GestureImageView page in GalleryViewPager.

Disallow an enlarged image to scroll in some case

Use OverScroller instead of Animator for better image fling (fast scrolling) experience.

Adjust the threshold where a picture will be deemed to be a long picture.

Bump version to 2.0.1

Update .gitignore to remove some temp config files

Update dependencies & suppress warnings