Add support for .f file lists

[DeeeeLAN]

Add support for .f file lists

[suoto]

HDL Checker has means to work out dependencies and compilation sequence, so all you should need is to let it know where the files are; there's support for config files hierarchy (so a component might have its own config file and the top level project only needs to include that), wildcards and relative paths, which solve most scenarios.

For cases where this is not enough, what I've done in the past is write a config generator script -- many languages have JSON libraries and that was one of the reasons I chose it.

The problem of supporting tool specific files is that vendors don't provide an open API to read and interpret them, so supporting them can be very time consuming because it's essentially chasing a moving target and I've steered away from.