Support RepeatEntry for ParameterRefEntry elements in EntryLists

[medley56]

Section 5.3.3 (p. 235) of https://public.ccsds.org/Pubs/660x1g2.pdf

RepeatEntry allows repeating of a parameter N times where N is possibly a previous parameter value. This could be useful when downlinking arrays of a predictable size.

The principle challenge here is how to represent a repeated ParsedDataItem with a non-unique name (maybe made unique by the repeat number?). Like anything else, if the repeat number is a reference to another parameter, that parameter must occur before the repeated parameter in the data structure.