Merge branch 'leongfeng-master'

Update javbus site url

Release v0.6.0

When fetching, skip magnets and covers that are already downloaded.

Release v0.5.1

Release v0.5.0

Fix issue raawaa#3

优先抓取高清磁链

updata readme

增加下载影片封面功能

add -b, --base option