Add tinyfsm, start converting core functions to an FSM-based event loop

lib/tinyfsm/doc/10-Introduction.md

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+Introduction
+============
+
+TinyFSM is a simple finite state machine library for C++, designed for
+optimal performance and low memory footprint. This makes it ideal for
+real-time operating systems. The concept is very simple, allowing the
+programmer to fully understand what is happening behind the scenes. It
+provides a straightforward way of mapping your state machine charts
+into source code.
+
+TinyFSM basically wraps event dispatching into function calls, making
+event dispatching equally fast to calling (or even inlining) a
+function. Even in the worst case, dispatching leads to nothing more
+than a single vtable lookup and function call!
+
+Key Features
+------------
+
+- Entry/exit actions
+- Event actions
+- Transition functions
+- Transition conditions
+- Event payload (classes)
+- Inheritance of states and action functions
+
+TinyFSM benefits from the C++11 template metaprogramming features like
+variadic templates, and does not depend on RTTI, exceptions or any
+external library.