A complete rewrite of the Overview section. The revised text
provides a more logical and comprehensive introduction to the
main concepts and capabilities of Zephyr, without providing
an excessive level of detail. (Those details should be provided
by the remaining sections of the Kernel Primer.)
This rewrite has also resulted in some small changes to the
About Zephyr and other Kernel Primer sections.
Change-Id: Idd4d5e0f0aabaaee8cd43d12563018ba4d8f7417
Signed-off-by: Allan Stephens <allan.stephens@windriver.com>