1, split render code to 3 files: __render_border.c, __render_bg_image.c, __render_text.c,

1, split render code to 3 files: __render_border.c, __render_bg_image.c, __render_text.c,
2, use GL_BLEND to show background-image when draw text,
3, scf: add scf_utf8_len() to get a UTF-8 char & its bytes,
4, css: support Chinese Char (中文) in border,
5, css: use macro ABC_CSS_BOX() to add HTML labels' attrs for css box model,
	ABC_CSS_SELECTOR() for css selector,
	ABC_CSS_BACK_GROUND() for back-ground attrs,
	ABC_CSS_FONT() for font attrs,
	ABC_CSS_TEXT() for text align, etc.
6, and render the margin of HTML objects transparent / clearing.