Minor but very important convenience feature, especially useful when
dealing with command-line apps. This now works:
magnum-imageconverter a.png a.jpg -c jpegQuality=0.75
The AnyImageConverter gets the jpegQuality option and then
automatically propagates it to the concrete plugin (which is either
JpegImageConverter or StbImageConverter), possibly warning in case the
target plugin doesn't recognize given option (i.e., doesn't list it in
its default configuration). Previously the user had to always specify a
concrete converter implementation using -C, which was rather annoying
and nonintuitive.
Because it's possible to specify the formats explicitly it doesn't make
sense not to support that. Eventually contents-based detection could be
implemented as well, but I don't want to do that just yet.
And make it return right after the first error. Also clean up some
old-style code -- the redirection should be restricted to the smallest
scope possible.
So if we convert foo.blah but explicitly tell it that it's a SPIR-V
file, it actually treats it as such, instead of complaining that `blah`
is not a known extension.
First step towards being able to operate directly on data.