v0.3.0: Date/time, regex, negative indexing, spread in calls

[shahadulhaider]

Summary

• Spec updated to v0.3.0 with 4 new feature sections
• 4 new conformance test suites: datetime (62 tests), regex (37 tests), negative_indexing (16 tests), spread-in-calls (15 new tests)
• Updated access.yaml negative indexing test (was error, now works)
• Fixed regex.yaml error substrings for case-sensitive matching

Features

• Date/time functions: now, parseDate, formatDate, year, month, day, hour, minute, second, millisecond, dateAdd, dateDiff
• Regex functions: matches, match, matchAll, replacePattern (RE2, function-based)
• Negative array indexing: items[-1] returns last element
• Spread in function calls: fn(...args)
• EBNF grammar updated for ArgElement in ArgList
• Future section updated to v0.4+