circular.hpp: Add read/write interface.

For usage with Console class for example.
Reword comment for clarity.
Add initial enumeration of Cortex-M core blocks.
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.
Add hwconfig for STM32.
Add initial support for LLVM MSP430 target.
Elaborate LLVM support for MSP430.
Add support for LLVM C backend roundtrip compile.
Fix one case were bitcode was still generated instead of LLVM assembly.
Add NearPtr class implementation - transparent offseted pointer of small size.

For example, allows to address up to 64KB of 32bit MCU with 16bit pointer
value. Useful when pointers need to be stored within in-memory objects.
Add NearPtr test.
First step towards switching to C++11.