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

lib/tinyfsm/doc/30-Concepts.md

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+Concepts
+========
+
+Keep it Simple
+--------------
+
+By design, TinyFSM implements only the very basics needed for
+designing state machines. For many people, it is important to know
+what a library is doing when making a decision for a specific library.
+
+
+State Definition
+----------------
+
+States are derived classes from a base FSM state, providing react()
+functions for every event, as well as entry() and exit() functions.
+
+
+Event Dispatching
+-----------------
+
+TinyFSM does not hold state/event function tables like most other
+state machine processors do. Instead, it keeps a pointer to the
+current state (having the type of the state machine base
+class). Dispatching an event simply calls the react() function of the
+current state, with the event class as argument. This results in a
+single vtable lookup and a function call, which is very efficient!
+
+Event dispatching on an FsmList<> are simply dispatch() calls to all
+state machines in the list.
+
+
+Header-Only Library
+-------------------
+
+The TinyFSM library consist entirely of header files containing
+templates, and requires no separately-compiled library binaries or
+special treatment when linking.