hmtl-loader 1.* compatibility

[peterpoe]

This add compatibility with html-loader 1.0+. Also, replaces html with more limited disruption of original code to avoid breaking other loaders that add code to html-loader (like file-loader).

[WearyMonkey]

Thanks @peterpoe !

I took some inspiration from your code, but decided on a slightly different approach that is backwards compatible and supports different variable names:

#88