This was found by cppcheck 1.6x used in Travis-CI, however this
seems to be a false positive, as it is not found by newer versions
of cppcheck.

Adding and correcting description/rational on why certain cppcheck
warnings or errors are intentionally suppressed.

Logic was swapping byte order on Big Endian platforms

For some reason the LLVM/clang version of `stdatomic.h` does not include
`stdint.h`, though it uses types from it.

The "verbose" alternative for assert() is now an expression and
can be used in all the places that a funcion call can be used.

g++ gives the error message "error: invalid conversion from ‘void*’ to
‘list_node*’ [-fpermissive]"

I applied the following terminology and changed the wording in the doc
accordingly:

* must not: If the parameter is of the value it *must not* be it either
  hits an assert or crashes the system.
* may not: The value can be that value, but the function will return an
  error.

Updated file comment header to comply with coding standard;
added brief module description and reference to tsrb to guide reader
who might be looking for thread-safe implementation

and improve docs for THREAD_FLAG_TIMEOUT