Initial Flex checkin

Flex aims to be a collection of portable and embeddable
network server components.

Including a server component from Flex should be as easy
as including the appropriate Flex header and compiling in
the relevant object files.

It should also be trivial to port Flex components to operate
on nearly any platform. The concurrency and socket primitives
are abstracted out from the core server logic.

Flex is meant to be statically included with C++11 projects.
In the future there may be a Flex shared library with a C
interface as well as a multi-purpose Flex executable.