Adrian Shum

implement vips_image_new_from_file

1

This enables creating new image object directly from file path, using [vips_image_new_from_file](https://www.libvips.org/API/current/VipsImage.html#vips-image-new-from-file): Below is the go bench of `NewImageFromFile` against the master branch. The memory difference `B/op` is very noticeable....

#178

This is a WIP of write stream implementation using [VipsTargetCustom](https://www.libvips.org/API/current/VipsTargetCustom.html).  Using this build, the memory usage of 6 instances exploded then starting to scale...