Properly set image MIME type when opening from a path (osiemsiedem#10)

Without this, format will always be JPEG if no format is explicitly specified. The expected behavior is that the format remains unchanged (PNG becomes PNG etc.).

Fix the way BlendMode is specified when dealing with transparent imag…

…es (osiemsiedem#8)

Use sequential access mode when "VIPS_ACCESS_MODE=sequential"

Couldn't find any other sane way of passing arbitrary options to this call

Merge pull request #2 from widewhale/fix-webp-error

Remove 'interlace' option from webp processing