Fix entity errors

[stevecheckoway]

Named character references in attributes whose last character is not ;
and for which the next input character is = (or ASCII alphanumeric,
but this isn't tested here), flushes the code points consumed as a
character reference without adding a parse error.

Named character references not in attributes whose last character is not
; are errors, regardless of the following character as noted in the
#new-errors section but without an entry in #errors, the number of
errors are wrong. (See
#107).

Separately, this adds the missing expected-doctype-but-got-start-tag
error.

[stevecheckoway]

Should the old error be a named-entity-without-semicolon instead of missing-semicolon-after-character-reference?