Support for buffered pack

[leetrout]

@mmadfox Would you be open to a PR to add support for packing in memory instead of the filesystem?

I'd like to have something like:

var b bytes.Buffer
if err := crx3.Extension("/path/to/extension").PackToBuf(b); err != nil {
    panic(err)
}
b.WriteTo(someHTTPResponseWriter)

[mmadfox]

Yes, this is a very good suggestion.

It seems to me this is more idiomatic WriteTo(io.Writer) than passing a Buffer. What do you think?

var b bytes.Buffer
if err := crx3.Extension("/path/to/extension").WriteTo(b); err != nil {
    panic(err)
}
b.WriteTo(someHTTPResponseWriter)

[mmadfox]

Added API for packing into a buffer. See the example

[leetrout]

Oh thank you very much!