Refined some MD2 descriptions.
Restricted RandomAdder to MoleculeBuilderDissectors.

This is required for convenient error handling. Technically, it's easy
to make it work with DissectorOs too, but there hasn't been a need for
that yet.
Implemented IndexOutOfBoundsException handling in RandomAdder
Got rid of special handling for empty files.

It's not necessary anymore. Instead, added handling for
IndexOutOfBoundsException (although it's pretty unlikely to occur).
Added an array dissector.
Refactored MD2 using array.
Put comments in proper places in MD2.