Release 0.4.2

[mciantyre]

We've accumulated non-breaking HAL changes, including three new peripherals:

• SRTC (Implement basic support for the SRTC #83)
• ADC (ADC Implementation #84)
• TRNG (Implement basic support for the TRNG #99)

I'm planning a 0.4.2 release of the HAL to publish these new peripherals. Once released, the new peripherals will be immediately available to users who typically target a 0.4 HAL crate.

I plan to release sometime next week. Should we hold off, or include any other work?

The ADC support will warrant a new release of the IOMUXC crate, which defines the ADC pins. I'll track that in the IOMUXC repo.

[mciantyre]

See the release notes here.