Add Maps to Orderly

Orderly doesn't define a map or dictionary kind of structure that we need for properties.

Orderly maps could look like this:

map

isAllowed; // keys are strings and values are booleans
map { string => union

} things; // keys are strings and values can be strings, integers or null
map

intMapping; // keys are one of enum values and values are integers

Grammar:

'map' '

' optional_optional_marker