fix deprecations with newer compilers

[MartinNowak]

• explicit switch fall-through
• replace currAppTick
• disable module cycle detection

[bFraley]

@MartinNowak Thank you so much for tending to this! I'm hoping @maximecb can take a quick look and give her approval to merge.

[maximecb]

@MartinNowak Is it no longer possible to get a microsecond timer? If so, that's unfortunate, because a millisecond timer will likely not be precise enough :\

[wilzbach]

@MartinNowak Is it no longer possible to get a microsecond timer? If so, that's unfortunate, because a millisecond timer will likely not be precise enough :\

I think you can do total!"usecs" and even total!"hnsecs" as Duration is internally kept as hnsecs. @MartinNowak just removed your function because it was unused.

[MartinNowak]

Yes, MonoTime internally uses whatever high-precision timer is available. It's no longer possible to get a high-precision time since app start.