Add simple test for CircularBuffer.
Add has_free_size() method.
Add read/write interface.

For usage with Console class for example.
Reword comment for clarity.
Add initial enumeration of MCU blocks.
Elaborate/fix typos.
Make .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.