0.6.12

• for loops over arrays are now converted to more efficient
  index-based iteration (#2831). This can result in significant cycle
  savings for tight loops, as well as slightly less memory usage.

• Add type union and intersection. The type expression

  T and U

  produces the greatest lower bound of types T and U, that is,
  the greatest type that is a subtype of both. Dually,

  T or U

  produces the least upper bound of types T and U, that is,
  the smallest type that is a supertype of both.

  One use case of the former is "extending" an existing object type:

  type Person = {name : Text; address : Text};
  type Manager = Person and {underlings : [Person]};

  Similarly, the latter can be used to "extend" a variant type:

  type Workday = {#mon; #tue; #wed; #thu; #fri};
  type Weekday = Workday or {#sat; #sun};