Report unfused functions

[harendra-kumar]

We should have an option to report the functions/constructors that did not get fused. This will be a big aid to programmers to know where the performance problems might be. Once we have this option, we can also replace the inspection testing in streamly with this plugin.

[harendra-kumar]

We have already added verbose modes to report what did not fuse. We just need to control those from the plugin command line options.

[harendra-kumar]

Other than command line options we also need a FUSED pragma to be used by programmers on top level functions that must not have any unfused constructors i.e. the the function has a closed loop which should be completely fused.

By looking at the FUSED pragma the plugin can tell if the function is supposed to be fused but has not fused.

[harendra-kumar]

Instead of using FUSED pragma I think we should use an UNFUSED pragma. So that the default is FUSED, to suppress the unfused warnings the programmer has to put the UNFUSED pragma.

This should be simple to implement as we are already reporting warning for all unfused cases, we just need to suppress it for UNFUSED annotated functions.