pfeatherstone

The other thing is the accuracy of `cyl_bessel_i()` which determines the accuracy of `kaiser()`. I've opted for a MUCH simpler implementation but it comes at the cost of some accuracy....

~~STFTs using kaiser window are now MUCH slower. I don't understand. I think it has something to do with the window now being a function object as opposed to enum....

I'll wait until master is updated with the C++14 stuff then I'll merge and this should pass the tests I think

I've made a basic change to the cmake scripts to enable C++14. Hopefully the tests will pass. I've noticed though that dlib is using pretty old cmake code and maybe...

@davisking I've merged master should be good to go

@davisking I've addressed your comments. Hopefully you like it.

I will have a look

Maybe we need to update CI/CD to build with 14, 17, 20

@VisionEp1 What's your system? Tried on Godbold with MSVC and it works: https://godbolt.org/z/qzcKEacdW EDIT: actually it only works with v19.latest. Curious. I hate windows

I have a fix https://godbolt.org/z/TEhqPa37e