Update MSP430 DriverLib to 2.91.13.01

[rei-vilo]

I wanted to use the RTC of the MSP430FR5994 but some files were missing from the MSP430 DriverLib supplied with Energia.

For example, Energia doesn't include rtc_c, when MSP430 DriverLib 2.91.13.01 does.

I wasn't able to determine the exact version of the MSP430 DriverLib supplied with Energia. The dates of the files suggest 19 Jun 2016. We are almost 4 years later, so a refresh would be great!

Once the MSP430 DriverLib was refreshed, implementing the RTC was fast and easy, thanks to the excellent MSP430 DriverLib for MSP430F5xx_6xx Devices - User’s Guide.

All MCUs should have the same level of quality for their documentation.

[rei-vilo]

When an updated MSP430 core is going to be released?

See #74, #87, #95, #120