Rename `hal.h` to `unistd.h`?

[mlund]

The usleep() function is usually found in unistd.h. Is there a reason it's in hal.h?

usleep(3)               Library Functions Manual               usleep(3)
NAME         [top](https://www.man7.org/linux/man-pages/man3/usleep.3.html#top_of_page)
       usleep - suspend execution for microsecond intervals
LIBRARY         [top](https://www.man7.org/linux/man-pages/man3/usleep.3.html#top_of_page)
       Standard C library (libc, -lc)
SYNOPSIS         [top](https://www.man7.org/linux/man-pages/man3/usleep.3.html#top_of_page)
       #include <unistd.h>

       int usleep(useconds_t usec);

[lydon42]

Because we have no unistd.h? Perhaps because it depends on counting rasters (this is because it should also work when in HYPPO mode, where stuff like CIA does not work as one would expect)?

[mlund]

My thinking is that the library tries to mimick libc and I'd like the interface to follow a path of least surprises. I guess HAL is short for hardware-abstraction-layer(?) and is probably not the first place one would look for usleep(). Not having a unistd.h is quickly fixed but if so, we should probably keep a working hal.h around and emit a deprecation warning if someone tries to use it. In any case, this is likely not a high priority.

[lydon42]

usleep is used a lot in the core utilities of MEGA65, but it is an easy change to switch to unistd.h. And it won't hurt the current state, as I pinned all of them to v0.2.0 because of the other changes.

So feel free to make it more compatible to the standard and we will switch the core when everything is in a stable state again.

And for compatibility we can keep a hal.h that include unistd.h and emits a warning.