Timer changes

If you're interested, I've applied the same timer changes I made to baseflight to cleanflight.
Unfortunately, I haven't been able to test them, and for some reason I get compile errors (in other files) when building for targets other than NAZE32. Timer.c compiles cleanly though. Anyway, I thought this might save you the job of merging in the changes yourself.
Feel free to try the changes out and incorporate them into your project if you're happy with them.
If you don't like them, just cancel the request.