deal with recursion problems by determining the shortest resolvable reference

[d0c-s4vage]

Grammar rules that generate lists work well for parsing, but are a pain when using them to generate data. E.g. from the python 2.7 grammar, there's the fpdef and fplist rules. Currently gramfuzz almost always runs into recursion errors when building the fpdef and fplist rules:

fpdef: NAME | '(' fplist ')'
fplist: fpdef (',' fpdef)* [',']

gramfuzz should be able to process all defined rules in a category and determine its distance from a leaf node, as well as each option inside an Or to determine which option gives the shortest resolvable path. This can then be used to determine the shortest-path to generating a rule without chancing recursion errors.