HTML declaration blocks do not follow spec 0.30

[notriddle]

HTML block condition 4 says:

Start condition: line begins with the string <! followed by an ASCII letter.
End condition: line contains the character >.

cmark only accepts it if it's capitalized (which is what 0.29 said, but was changed in the current spec version). The first line is parsed as an HTML block, but the third line isn't, and it should be:

<!X

>

<!x

>

[notriddle]

Wrong repo. Sorry.