Add maps/objects to VeLa

[dbenn]

Maps (dictionaries) are useful for all kinds of reasons.

Objects would be useful for encapsulating all the features of a ValidObservation, e.g. when used in a filter as well as in general coding. Nothing fancy. Just objects, potentially aggregating other objects vs inheritance or interfaces, although I wouldn't rule out interfaces, i.e. ADTs. So, more object-based than OO.

Ability to access member via m.[str] or m.ident.

Add an object construct, starting with maps. Keys in maps can have any value at all, including functions. Some syntactic sugar may help to objectify, e.g.

m <- map { x: 2  f: function(n:int):int ... }
a <- m["x"]
a <- m.x  -- same as above
b <- m.f(42)

Implicit or explicit reference to map/object available to map/object function calls (this, self, me, my)?

m <- map { x: 2  f: function(n:int):int { this.x*n } )  -- implicit
b <- m.f(42)  -- 84

To achieve this, a function in an object could have a this variable -- m in this case -- added to the current scope.

Could use struct instead of map but latter is more general and powerful and we want to avoid a proliferation of data structures.

Release with a motivating example eg via filters, TG (e.g. maintain heading state).

[dbenn]

See also #201