Make thumb streamable

[mlegenhausen]

This would be nice for generating thumbs on demand. Getting a file stream in and write it out.

What I expected:

gm(readStream).thumb(320, 160).stream().pipe(writeStream);

[jonathanong]

i'm considering removing this helper. is it possible for you to use native arguments instead? http://www.imagemagick.org/Usage/thumbnails/#cut

[mlegenhausen]

I used scale instead and it works as expected.

[jonathanong]

so you were able to do this without gm().thumb(), correct?

[mlegenhausen]

Yes so it would be the best to remove thumb and add an example how to create thumbs instead, cause it is a common operation.

[jonathanong]

good to know. adding it to the list of things in v2: https://github.com/aheckmann/gm/wiki/Future