Performance: date parsing

Current date parsing code [Parser.EventDateParse, and Parser.DateTokens] is string based, rather than char[] driven. Investigate a GEDSplitter like system, may have to use **Trie**s for calendar, month, keywords and other lookups. Would be nice to eliminate getsubstring and other string calls.

Start by reading Parser.EventDateParse and Parser.DateTokens to understand the current string-based date parsing path. Investigate whether a GEDSplitter-style, char[]-driven approach and Trie lookups are suitable; done means agreeing on and implementing a measurable reduction in substring and other string calls.

Written by the indexing model from the issue text.