Create simple HTTP ETags

Highly inspired from https://github.com/jshttp/etag , almost all the code and the documentation is taken from that project, all I did was to port the project over to dart.

API

etag(entity, {bool? weak})

Generate a strong ETag for the given entity. This should be the complete body of the entity. Strings, Uint8Lists, and FileStat are accepted. By default, a strong ETag is generated except for FileStat, which will generate a weak ETag (this can be overwritten by weak).

weak

Specifies if the generated ETag will include the weak validator mark (that is, the leading W/). The actual entity tag is the same. The default value is false, unless the entity is fs.Stats, in which case it is true.