Make const-fn default #153
Description
At the moment the cortex-m still hides const versions of some functions (especially Mutex::new()) behind the const-fn feature, but these have worked on stable Rust for some time now.
It looks like this crate does not yet follow the WG MSRV policy so I'm not really sure what the MSRV even is, but perhaps we could allow it to be 1.31 and therefore either remove the const-fn feature or make it a default.