Introduced TY_(IsHTMLSpace)(uint c), which checks to see if c is one of the
chars that the HTML spec (and browsers) treat as a space in attribute
values: 0x020 (space), 0x009 (tab), 0x00a (LF), 0x00c (FF), or 0x00d (CF).
Can't use ANSI C isspace(int c) here because like standard functions for
many other langs, it also treats 0x00b as a space.