Support for Scheme vector literals

[noahvanes]

Vector literals in Scheme (e.g., #(1 2 3)) are currently not supported.

In order to do so, the SExpParser will first need to be extended to support this notation.
Then, adding the corresponding evaluation rules in the concrete and abstract interpreters should be trivial.

[bramvdbogaerde]

The S-expression parser has been extended in 3d39320, vector literals are now parsed into SExpVector instances. The corresponding evaluation rules still need to be implemented in the concrete and abstract interpreters.