Add stm32l0xx-hal crate (#185)

I'm not the author, but I'm using this crate and the parts that I tested seem to work fine 🎉

README.md

@@ -225,6 +225,9 @@ Also check the list of [STMicroelectronics board support crates][stm-bsc]!
 - [`stm32f4xx-hal`](https://crates.io/crates/stm32f4xx-hal) - ![crates.io](https://img.shields.io/crates/v/stm32f4xx-hal.svg)
    - Generic HAL implementation for all MCUs of the stm32f4 series
 
+- [`stm32l0xx-hal`](https://crates.io/crates/stm32l0xx-hal) - ![crates.io](https://img.shields.io/crates/v/stm32l0xx-hal.svg)
+   - HAL implementation for the the STMicro STM32L0xx family of microcontrollers
+
 - [`stm32l1xx-hal`](https://crates.io/crates/stm32l1xx-hal) - ![crates.io](https://img.shields.io/crates/v/stm32l1xx-hal.svg)
 
 - [`stm32l151-hal`](https://crates.io/crates/stm32l151-hal) - ![crates.io](https://img.shields.io/crates/v/stm32l151-hal.svg)