upgrade v1.2.1

improve BlurImpl detection and add fallback impl

upgrade version to 1.2

support both android support library and android x

update gradle and buildtool (use gradle wrapper)

upgrade v1.1.2

draw overlay color in rect

upgrade v1.1.1

add samples

fix downsample factor when blur radius is very large

upgrade android studio 3.0

improve readme

improve readme

upgrade v1.1.0

ignore OOM error when create bitmap