port to RTFM 0.4

[hdhoang]

Hello hello!

The next cortex-m-rtfm is out. But it is a major rework, so I would like to propose a roadmap.

Short-term, I would like to release the current PRs (#76, #77, #78) as follow:

• [x] fork ykomatsu's PR into a protected branch under either of our accounts
• [x] rebase and publish releases at each step

Long-term involves porting to cortex-m-rtfm 0.4

• [x] Fix the crate into 2018 edition (a requirement for rtfm 0.4, and can be started now)
• [x] Wait for svd2rust 0.14
• [x] Wait for the next stm32l1 made with svd2rust 0.14
• [x] Bump stm32l151-hal
• [x] Rework with cortex-m-rtfm 0.4

Going forward, the embedded WG is working on books and documentation based on these newer crates. The porting effort is not easy, but I hope clearer documentation can bring in more interest. I intend to hook up an st-link v2, and if budget allows even get another AP1.

[hdhoang]

There's a new stepping stone on the way: @stm32-rs is working on multi-device HAL crates, in the style of stm32-rs/stm32-rs. For the AP1 they have https://github.com/stm32-rs/stm32l1xx-hal. It's a bit different from yours, so I'll need a bunch of reading to figure out what's what. ~It also lacks the DMA module which I hope to help out with too.~

The main benefit will be tracking closely with the stm32l1 crate.