making _.unescape be able to unescape ' and ` escaped in Dec format

Let's have underscore unescape &#39; and &#96; These are valid HTML entities for ' and ` symbols.
Any browser works both with Dec and Hex representation of these symbols.

The issue is that Django web framework escapes ' and `  using Dec approach. And most probably other frameworks may do the same way.

So in such situation it's necessary to write some additional code which should probably be inside of the library.