add *.xccheckout to gitignore
issues #2834:Use Android standalone toolchain on windows to remove the dependence of cygwin
Merge pull request #3854 from pktangyue/patch3

add *.xccheckout to gitignore
Update AUTHORS [ci skip]
issues #2861:fix memory leak when loading plist file using SpriteFrameCache.
issues #2774:AssetsManager Test downloading progress label not sync with actual download.
Merge pull request #3857 from Dhilan007/develop

issues #2834:Use Android standalone toolchain on windows to remove the d...
modify download addresss in README
Merge pull request #3863 from minggo/change-download-addr

[ci skip]modify download addresss in README
various other changes