This adds implementations of some standard procedures:

* call-with-bytevector-output-port
* get-bytevector-n
* open-string-output-port
* call-with-string-output-port
* bytevector-u8-ref
* bytevector-s8-ref
* bytevector-u32-ref
* iota
* string-join
* vector-binary-search
* quotient
* remainder
* utf8->string