Add Antlr grammar for date pattern

Author: zhossain-info

src/main/java/com/relogiclabs/json/schema/grammar/DateTimeLexer.g4

@@ -0,0 +1,47 @@
+lexer grammar DateTimeLexer;
+
+ERA : 'G';
+
+YEAR_NUM4 : 'YYYY';
+YEAR_NUM2 : 'YY';
+
+MONTH_NAME : 'MMMM';
+MONTH_SHORT_NAME : 'MMM';
+MONTH_NUM2 : 'MM';
+MONTH_NUM : 'M';
+
+WEEKDAY_NAME : 'DDDD';
+WEEKDAY_SHORT_NAME : 'DDD';
+
+DAY_NUM2 : 'DD';
+DAY_NUM : 'D';
+
+AM_PM : 't';
+
+HOUR_NUM2 : 'hh';
+HOUR_NUM : 'h';
+
+MINUTE_NUM2 : 'mm';
+MINUTE_NUM : 'm';
+
+SECOND_NUM2 : 'ss';
+SECOND_NUM : 's';
+
+FRACTION_NUM06 : 'ffffff';
+FRACTION_NUM05 : 'fffff';
+FRACTION_NUM04 : 'ffff';
+FRACTION_NUM03 : 'fff';
+FRACTION_NUM02 : 'ff';
+FRACTION_NUM01 : 'f';
+
+FRACTION_NUM : 'F';
+
+UTC_OFFSET_TIME2 : 'ZZZ';
+UTC_OFFSET_TIME1 : 'ZZ';
+UTC_OFFSET_HOUR : 'Z';
+
+SYMBOL : [!-/:-@[-`{-~]+;
+WHITESPACE : [\n\r\t ]+;
+
+TEXT : '\'' ( ~'\'' | '\'\'')* '\'';
+