Added Stream functionality

[angedelamort]

• Can now call Compute and Append with a Stream
• The field in SafeProxy is now really read-only.
• No unit tests were written for streams since all the current tests already test the Stream.
• With a Stream, you don't need to have offset/length overload functions since it's already contained in the Stream.
• To Debug the buffer in a MemoryStream, ensure that the last parameter of the constructor is true.

[angedelamort]

It's my first pull request on github, so I'm not sure if everything is correct... but seems simple enough.

I've asked for the feature (in issue) but decided to make the change instead since I wanted to have it.

[force-net]

Ok. Thank you, when I find the time to update code, I'll review and merge your PR.

[angedelamort]

Just found out a use case where my modification doesn't work well with a Stream. I did my test thinking about a MemoryStream where it's easy to create a "sub" buffer using parametrized constructor, but in most cases, the Stream sub class won't have this feature. Also, in most case, it should be ok as it is, but again, since doing the change, it should support the same feature as the buffer (providing the offset and length -> Compute(Stream, long, long)). For example, if you want to calculate de CRC32 of the 1024 first bytes of a file. I'll try to address that in a future pull request. Thanks