Edits the metadata inside a PNG without re-encoding it, as Storehouse.Image.JPEG does a JPEG's: the same changes, the same tags.

A PNG keeps its metadata in chunks of their own: Exif (eXIf), XMP and text (iTXt, tEXt, zTXt), the time (tIME). These functions rewrite those chunks, each with its checksum, and copy every other one, the image data and what draws it (palette, transparency, colour profile, an APNG's frames), byte for byte.

• strip: :gps - the Exif GPS directory, zeroed, and XMP's GPS properties. The "Raw profile type" text chunks ImageMagick writes, Exif and XMP again in hexadecimal, go too.
• strip: {:keep, tags} - Exif with only the tags named, the text chunks of those tags (Author, Copyright, Description), and no other text, XMP or time.
• put: %{artist: _, copyright: _, image_description: _} - written into Exif, and as the text chunks Author, Copyright and Description that PNG readers show, in place of any before them.

edit_file/3 reads only the metadata chunks into memory. A PNG whose chunks cannot be read is refused with {:error, :malformed}, one whose Exif cannot be read with {:error, :malformed_exif}.