Moved 2 syntax and 3 selectors tests into their better,
more appropriate folders, along with their associated
reference files.

--HG--
rename : css21/reference/first-letter-selector-028-ref.xht => css21/selectors/first-letter-selector-028-ref.xht
rename : css21/first-letter-selector-028.xht => css21/selectors/first-letter-selector-028.xht
rename : css21/first-letter-selector-029.xht => css21/selectors/first-letter-selector-029.xht
rename : css21/first-line-selector-017.xht => css21/selectors/first-line-selector-017.xht
rename : css21/escapes-015.xht => css21/syntax/escapes-015.xht
rename : css21/escapes-016.xht => css21/syntax/escapes-016.xht