v0.1.3

Changelog

151423b Add Speed,Avg Speed,Total cost times output.
9e36aad Download no longer needs its own lock
8c6db2f Merge #11
c1c7cf0 Merge #12
de7f804 Merge branch 'kingwrcy-master'
3ad1c2d No need to keep track of the temporary directory
6e452dc No need to use pointer to channels
02ec844 Update README.md
df11970 Update filename.go
d4d74c2 Use atomic instead of mutex for concurrency safe size updating
aaf2df1 Use context with cancel to stop a goroutine
770bc1e Use errgroup to ease error handling in goroutines
e1716ba Use https as the default scheme if scheme is not given
286c77a fmt, clean code, use atomic in progress.