RUST-527 - Implementation of gridfs

[Stargateur]

This is a work in progress implementation of gridfs. The jira ticket RUST-527. Any help/remark/critic are always welcome. I will update this according to my progress:

• Basic Structure
• Add features to avoid include it in crate that doesn't need it gridfs
• Require to be able to create index, RUST-273: Implement Create indexes #188
• Should we implement MD5 ?
• ?

[Zageron]

Is this stale? Does this driver support gridfs?

[kmahar]

Hey @Zageron! At this time the driver does not support GridFS. This PR has been inactive for a while but we've left it open in case the original author or anyone else is interesting in resuming work on it!

To respond to a couple of the points from the original PR -

• The driver has an index management API now which was added in version 2.0.0.
• We should omit MD5 support in a Rust implementation as per the GridFS specification it has been deprecated and should not be supported in new implementations (see Design Rationale section.)

[kmahar]

we currently have implementation of GridFS in progress (so far a sketch of the public API has been merged in #688), so I am going to close out this pull request. thanks for the initial work on this @Stargateur!