Rename the macro used to build up the debug message, to better reflect
its generality.
It can be used anywhere to build a string with C++ stream formatting.
std::string s = EMPER_BUILD_STR("foo = " << 1 " , bar = " << bar(42));

Since WDBG was the only log macro without a terminating newline, which
was in fact broken according to flow, we can remove it and the new line
handling code in the LOG macro.

In debug builds, the schedule() method is now guarded by an assert(),
as due to this change, the schedule() method will no longer work from
everywhere.

This also improves the worker sleep method.

to aid debugging.

We need to spawn another fiber in fibKickoff