Adding a template tag to generate query strings

So I think I ran into an issue that we might consider before we release 5.1. One thing that I now ran into is that I would like to specify a variable for a key, ie

{% query_string some_var=some_other_var %}

which is currently not possible and if we added it later on would be ambiguous when manually setting strings. The only thing I can think of is change the behavior to:

{% query_string 'page'=some_other_var %} &
{% query_string page=some_other_var %}

So essentially literal keys would need quoting. This is rather ugly, but I still would like to throw it out here for (re)consideration.

/cc our fellows @nessita @sarahboyce for visibility.