update dependencies

Any chance of updating some dependencies? The one that is causing me trouble is `cortex-m-rt` which I would like moved from "0.6.7" to  "^0.7.0". That also requires moving `stm32l1` from "0.5.0"to  "0.14.0". These cause version conflicts for me because other crates are using newer versions.  I see `cortex-m` is also pretty old.

These do all require some code updating too.
