Convenient initialisers from ByteBuffer

[Davidde94]

Added simple initialisers to various types that consume a ByteBuffer.

Motivation:

Common operations to read a ByteBuffer as some different type T were a little too verbose.

Modifications:

New initialisers for:

• Data
• String
• [UInt8]

Result:

var buffer = ...
let string = String(from: &buffer)
let data = Data(from: &buffer)
let array = Array<UInt8>(from: &buffer)

[Lukasa]

I think we don't need the separate files for each of these: they can all go in ByteBuffer-aux except for the Data one which can just go next to readData.

[weissi]

Thank you! This looks very useful, left a few comments

[Lukasa]

Teeny tiny notes here, this patch looks great otherwise.

[weissi]

Awesome, that looks great!

[Lukasa]

LGTM, thanks!

[ktoso]

Whoop, missed review here -- sorry fixed my email settings / filters a bit recently :-)

LGTM, really nice to see this one