perf_counter.hpp has backing store, so goes to rtos/.
Use timer::elapsed() for time calculation.
Add accumulating perfcounter.
Hw-configize and add PerfAcu example.
Dispatch on target for correction factor.
Elaborate MSP430 blocks definitions, for generalized IRQ routing support.
Add generilized IRQ dispatching for MSP430.

Supports timer, uart, spi.
UART is on USCI_A specifically.
Add hardware SPI definition.
Add example of general IRQ dispatch.

So far supported only on MSP430.