Equality semantics not defined in the spec

Only `std.primitiveEquals` is defined, but not full equality.

Equality behaves in a fairly intuitive way, but it still should be described. There are certain boundary cases, e.g. the short-circuiting when checking object equality:

```
{
a: 1,
b: function() 42
} == {a: 2}
```
vs
```
{
a: function() 42
b: 1,
} == {b: 2}
```