Show problematic html under error (proof of concept)

I don't know how to figure out the line out of a buffer so this only works on one-liners like after the out of [gulp-compressor](https://github.com/steel1990/gulp-compressor), but this is the output.

	[14:00:28] HTML Error: index.html Line 1, Column 2928: End tag had attributes. 
	xit" type="button"></button type="button"> </div>  
	                                        ^

I thought it would be good to show the code like the official validator does since my html files are usually preprocessed by templating systems, mainly.