make sure index in range[0, cellCount)

make sure index in range[0, cellCount)

add isTapEnabled

add property isTapEnabled

bug fix: firstVisibleCell may not correct when Carousel frame is zero

bug fix: firstVisibleCell may not correct when Carousel frame is zero

bug fix: firstVisibleCell may not correct when Carousel frame is zero

bug fix: firstVisibleCell may not correct when Carousel frame is zero

add support didTapAt

add support didTapAt

add support didTapAt

add support didTapAt

support swift 3

update code and api to support swift 3

support swift 2.3

support swift 2.3

refactor code(api has changed)

refactor code and bug fix

a, refactor code and rename api to make api clear
b, fix progress error
c, improve paging

fix bug and optimize

1, fix crash if CarouselView init size is zero by restrict page width, page height to not less than 1(to avoid dived by zero)
2, add miss delegate method of scrollViewDidEndDecelerating
3, make pagingEnabled, pagingRequired more clearly