Dead tests revived
Introduced `presentMissingProperty`
Refactored `t_updateLookupWithKey`
Refactored `t_update`
Refactored `t_updateWithKey`
Refactored `t_splitLookup`
Refactored `t_insert*`
Refactored `t_null`
Added `t_size`
Refactored `t_lookupXX`
Refactored `t_fromList*`
Refactored two-map functions
Refactored `t_isSubmap*`
Refactored `t_unions*`
Refactored `mapAccumWithKey`
Refactored `t_from*AscList`
Introduced `equal`
Introduced `internal`
Introduced `above`
Replaced `direction` by `onLeft`