Add a single makefile such that it will rarely need modifications
with regular source code changes.

The usual configure step for build environment detection is done
manually by editing config.mk, it is expected to be simple make
variable changes (mostly CFLAGS), later a simple configure script
can be added to generate config.mk if necessary.

Update the README.

Use standard name for the LICENSE file.

Use consistent license text across files:
- "ARM" is changed to Arm,
- "All Rights Reserved" is dropped (not needed),
- "This file is part of.." is dropped,
- Text is formatted as is recommended by the LICENSE file.