- remove destination file before attempting move from temp directory
- added shouldOverwrite property
call progressiveDownloadProgress in main queue
Fix where files are not moved from temporary path to targetPath when completion blocks are not set.
Merge pull request #19 from SpacyRicochet/master

Fixes issue #18.
Merge pull request #16 from fengjian0106/patch-1

call progressiveDownloadProgress in main queue
Merge pull request #12 from xinsight/master

Avoid 'file exists' error if file has been previously downloaded
Merge remote-tracking branch 'upstream/master'