Ticket 197: Editorial: Add more examples for new features

Regions that need examples:

• Error raising and catching.

• Byte vector section.

• File processing.

• Parameterizing current-*-ports.

• Third argument for assoc.

• square.

• list-copy, string-map, vector-copy, vector-fill!, vector-map, vector-copy!, string-copy!.

• digit-value.

square: done

list-copy: done

string-map: done

vector-copy: done

vector-fill!: done

vector-map: done

vector-copy!: done

string-copy!: done

digit-value: done

assoc: done

Bytevector examples: done

Exception examples are in #362. File examples and current-*-port examples still needed.

current-*-port example provided under get-string-output.

I'm not going to bother with file procedure examples. No other Scheme standard has them either.