More flexible candidate filtering

[kimci86]

At the moment, a candidate internal password representation is considered to be a solution if it verifies a conjunction of predicates.
Each of those predicates check if a fixed piece of data is at a fixed offset in the deciphered data produced by the candidate internal password representation.

It could be made more flexible like so:

• specify several acceptable offsets for a fixed piece of data
  • a set of offsets, a range of offsets
    • example: offset 10 or offset 20
    • example: offset between 30 and 40
  • absolute or relative to the end or relative to other pieces of data (partial order)
• specify several acceptable pieces of data at a given offset
  • a set of pieces of data
    • example: "abc" or "def"
  • regular expression?
• a mix of both
  • a product
    • example: "abc" or "def" at offset 10 or 20.
  • a disjunction (more specific, subset of the product)
    • example: "abc" at offset 10 or "def" at offset 20.

This suggestion comes from the discussion in #66