Limit total file size and chunk size

[nerg4l]

Would be great to have options for limiting total file size and chunk size. The handler should not accept files and chunks bigger than the limit. In some cases this could prevent malicious usage.

[nerg4l]

Related #44

When using Resumable.js, Flow.js, or simple-upload.js the last chunk can be bigger than the chunkSize parameter. Max twice as big but it is not defined in any of the mentioned libraries' documentation.