3.0 beta 12

• [new] Added a way to specify custom retry logic when network error happens #386
• [new] Improve disk cache migration performance #391 chuganzy, #394 nguyenhuy
• [new] Adds support for using cell vs. wifi in leau of speed for determing which URL to download if speed is unavailable. garrettmoon
• [new] Uses BPS minus time to first byte for deciding which of a set of URLs to download. garrettmoon
• [fixed] Fixes an edge case when image returned with 404 response, we now treat it as image instead of error #399 maxwang