[Feature Suggestion] Headers are always on a new line

[bkuhl]

When using this library I ran into challenges when parsing web page's HTML where headers were not always on a new line. I wrote a regex to adjust this so that it was always parsed correctly. I'm posting this issue here in case someone wants to adapt it to this project.

    public function headersNeverAtEndOfLine(string $markdown) : string
    {
        // any non-whitespace charcater
        $regex = "([\S])";

        // don't match pound signs that are part of a markdown link, are already next to a newline
        // or are part of a larger markdown header, such as "##### My Header"
        $regex .= "[^\n(#]";

        // match h1-h5 equivalents
        $regex .= "(#{1,5})";

        return trim(preg_replace("/".$regex."/", "$1".PHP_EOL."$2", $markdown));
    }

And then the test to show what this is actually doing:

    /** @test */
    public function verifyHeadersNeverAtEndOfLine()
    {
        $original = <<<EOF
This is a quick # Header test to ##See how
### Headers are #### Never at the end of an #####Existing line
EOF;
        $expected = <<<EOF
This is a quick
# Header test to
##See how
### Headers are
#### Never at the end of an
#####Existing line
EOF;

        $this->assertEquals($expected, $this->parsesMarkdown->headersNeverAtEndOfLine($original));
    }

[aidantwoods]

Hey there! I think we'll probably stick with CommonMark here – i.e. require atx headings to start on a new line for compatibility, but thank you for the suggestion anyway :)