Move to AWS signature V4 (required for eu-central-1)

[ghost]

This pull request (for commit 95f8cab) adds support for AWS V4 version.
Example:
$ s3fs BUCKET MOUNTPOINT -o endpoint=eu-central-1,url=https://s3-eu-central-1.amazonaws.com
You can checkout it here https://github.com/caxapniy/s3fs-fuse/tree/1.77v4merge

I have modified version https://github.com/shunataws/sv4s3fs
Changes:

• removed hardcoded China S3 servers, added command-line argument "endpoint"
• added content-md5 checking
• added multipart upload support

I was not able to merge branches - there are conflicts(caused by changes in HEAD)
Hope this request helps someone to merge changes to HEAD.

[ggtakec]

Hi, Wang

Thank you for PR, and I will start to check codes because many changes in this request.
But Github(web) said "could not merge automatically", If you can, please merge our master branch to your caxapniy/s3fs-fuse.
(I think it make automatically merge after that....)

It aside, I try to check the codes, please wait.

[ggtakec]

Hi, Wang

I merged your tree to dev_sv4 branch, the new codes is added with #ifndef SIGV3.
This branch is development for sv4 now, because AddSseKeyRequestHead() is needed to modify for sv4 yet.
After this merging, I'm working for coding, removing ifdef and testing.

Please wait for about a week.

Last, I close this pull request,
Thanks,