Proper string quoting in serialize(), "eel" format

When serializing to the "eel" format (expressions that can be
compiled into initializers by the EEL compiler), instead of
just adding quotes to strings and dstrings and hoping for the
best, we use quote() from the new "strings" module to actually
encode strings properly, in case they contain control codes,
double quotes and other nastiness.

Refactor:
	Renamed BIN_BOOLEAN as BIN_BOOLEANT, to make it more
	clear that it's actually a byte code for "boolean with
	value 'true'," and not just a type code.

	serialize() and deserialize() now use argument default
	values instead of the old 'specified' + local variable
	hack. (No difference for callers.)

Closes #30.