Missing MonoTimer:new as pub fn

[vortex314]

While the function is created in https://github.com/rust-embedded-community/tm4c-hal/blob/master/tm4c123x-hal/src/time.rs
,the function is not exposed, so also Instant cannot be obtained.

92 |     let mut mono_timer  = MonoTimer::new(cp.DWT, clocks);
   |                                      ^^^
   |                                      |
   |                                      function or associated item not found in `MonoTimer`
   |                                      help: there is a method with a similar name: `now`

Complete code : https://github.com/vortex314/tiva-rs

[thejpster]

I haven't touched this in five years. Feel free to send a PR and maybe some people can look at it.