Casting data types

[RyanBalfanz]

Add functionality to define casting types. For example, we may store a dictionary mapping a pattern to match with a callable. Then the casting may be as simple as map(pattern, callable).

{
RECORD_TYPE: str,
SAMPLE_BITS: int
}

If in the event that the pattern is not matched we may attempt to auto-detect type or a default callable (probably str).

I believe that either the PDS Standards Reference or Planetary Science Data Dictionary (See Wiki) provide information defining the type of many common PDS labels.