compile-frame with pre-decoder method

[d-t-w]

Hi Zach,

Currently compile-frame supports pre-encoder and post-decoder methods to manipulate the data-structure before/after use with a codec.

I'm currently using a third scenario - a pre-decoder method which manipulates the ByteBuffer being passed to a codec before decoding.

This is useful to me, because the RFC-5322 spec supports un-folding of headers before parsing, and I do that pre-decode.

A different solution would be to have a look-ahead style String codec which interpreted some byte sequences "\r\n\ " and "'\r\n\t" as simple space characters, but that seems more complicated, particularly as those byte sequences are super-sets of the "\r\n" delimiter.

More information here:
http://derek.troywest.com/articles/by-example-gloss/#gloss-extension

I could just parse my ByteBuffers prior to using the codec, but it seemed useful to append this transform method to the codec itself.

Again, I'm happy to supply a pull-request if you think it suitable.

Ta,
Derek