Improve handling of extra spaces and <cr> with blockquote

[Boris Berenberg]

Expected:

Words
> Quote
Words

Should render with only the word Quote as part of the blockquote.

Result:

Quote and Words are both blockquoted.

Side note: there seems to be no way to break out of this. I have tried:

<!--- -->
<!>
<br>

[Boris Berenberg]

caused by extra white spaces, and carriage returns inserted at the end of a line, instead of the beginning.