Contrib guidelines: elaborate/fix typos.
Mark .o as precious.
Add irq_reset() handler.
"lm4" target was renamed to "tm4".
Initial support to enumerate TM4 blocks.

Required for IRQ dispatch.
Refactor and generalize IRQ dispatch support to be reusable for other MCUs.
Add initial IRQ dispatching support for Cortex-M.
Add simplified (one handler) IRQ dispatch sample.
Update for IRQ dispatch refactor.