ENH: #2679 - DataFrame.to_html() urls_as_links parameter.
New urls_as_links boolean paramater that will output urls as href html
links. ref #2679 

Thanks for @tdas14 for initial code.

@TomAugspurger (I recall you doing some work on conditional html formatting, though orthogonal to this affect API)
 @lexual can you rebase
 @lexual can you rebase / update
 pls see comments on #9880 
 IOW this needs to have a global option (that defaults to `False`)
 closing, but if you would like to continue working on this pls reopen
 I have rebased, but don't have permissions to re-open I believe.

Please advise next steps to get it merged.

Apologies for long absence ;)
 https://github.com/lexual/pandas/commit/49992e9c5b5edfe9880d93466df4d448f3add5db

rebase @jreback 
 @lexual this is more appropriate as a method in `df.style` for #10250 

e.g.

`df.style.show_urls_as_links()` or something. You want to do a PR against @TomAugspurger branch for that?

And the idea is that a style can be created that can be `.set` as a style (or a default), so you can simply 'use' a style as the default and build on it.
 @lexual let me know if you want to do that PR agains my branch in #10250, it will actually be quite simple thanks to jinja.

Right now in the Jinja template I've got [a check](https://github.com/pydata/pandas/pull/10250/files#diff-871722e2eeea86e2eb7c981fa3748d4fR113) for if the value is a number or not. Jinja has a [urlize](http://jinja.pocoo.org/docs/dev/templates/#urlize) filter that you can apply to the else block.

We will need a more general way of applying arbitrary tags / modify the template, but that could work for now.
 @TomAugspurger yep, I'll try to take a look when I get a chance.
