Added mimetype guessing

[markunsworth]

Have added the option to guess mimetypes when uploading files. Uses much the same logic as S3cmd, have not implemented mimemagic logic.

Uses the same flags as S3cmd.

-M or --guess-mime-type

Fixes #67

[kennu]

This would be quite useful. I just broke my website by replacing aws s3 sync with s4cmd dsync, because it reset all the content types to application/octet-stream.

[markunsworth]

fixed up merge issues and reverted the formatting changes my IDE made

[schellj]

I merged this branch into my fork and it seems to work fine. Very helpful for my project as I'm recursively pushing a large number of files from a directory and my site wouldn't work if I uploaded with s4cmd without specifying the mime type for each file individually.

[Epsiloncool]

It looks like this change was not yet applied. This is a reason why I still have to use old slow s3cmd.
May someone please apply mime-type guessing change?

Thanks.

[shapirus]

bump.
it's not possible to use s4cmd as a replacement for s3cmd for recursive uploads without this option.

[dmitry-sinina]

I have same problem - it is not possible to use s4cmd for static site content upload without this patch.

[shapirus]

I have same problem - it is not possible to use s4cmd for static site content upload without this patch.

as a workaround, you may want to check https://github.com/peak/s5cmd
that's what I ended up using.