Customizable animation

• Fixed bug about pop twice #17
• Made it possible to customize animation #17
• Thanks @winddpan for contributing😍

Support iOS11 / Xcode 9.4.1

1.5.0

update podspec

refactor Demo project for Xcode 8.2.1

Merge pull request #13 from WorldDownTown/update_podspec

update version in podspec