Added internal support for an auto-expanding buffered reader, allowing for truly infinite lookahead.  Changed lexer.New() to default to auto-expanding.  Added contructor NewSize(), which replaces previous New(), accepting a readerBufLen parameter.  Also added additional constructors NewFromString() and NewFromBytes() which allow you to deal with fixed-length input.  Added Match*Func() functions which take a call-back function to validate the runes.  Added MatchMinxMax*() functions to allow control over the number of runes that match.  Modified word_count example to use NewSize(), and to deal with words longer than readBufferLen.  Moved internal function runesContainRune() into external function go_pkg/runes.IndexRune()