refactor code
add blank docs
rename 'parser.py' to 'parsers.py'
start global refactoring
define 'day_period' grammar
convert 'grammar' package back yo module
define 'time' grammar
define 'event_time' grammar
define 'date' grammar
define 'date_time' grammar
define 'float_number' grammar
define 'event_pos' grammar
define 'toggle_value' grammar
define 'callsign' and 'enemy_callsign' grammars
define 'seat_number' grammar
extract 'printable_word' grammar
extract 'aircraft' grammar
update definition of 'printable_word' and 'aircraft', remove 'enemy_callsign', add definition of 'enemy_aircraft'
define 'static' grammar
define 'bridge' grammar