Add the following query options: "review articles only", "search on a specific language"

[amchagas]

Hi there! Thanks for setting up Scholarly! We are using if for one of our own projects and after a bit of use, we found the need to add some more features into the query options. Namely, we introduced code to allow users to:

• Search for review articles only (which translates into "as_rr=1" in the googlescholar URL).
• search for things in a specific language (which translates to "lang_en" in the googlescholar URL in case searches are done for things in english language).

I did not complete the entire checklist as I was not entirely sure on what would be the best way to do that.. sorry! Happy to work more on it if someone points me in the right direction..

Checklist

• [x] Check that the base branch is set to develop and not main.
• [x] Ensure that the documentation will be consistent with the code upon merging.
• [ ] Add a line or a few lines that check the new features added.
• [ ] Ensure that unit tests pass. If you don't have a premium proxy, some of the tests will be skipped. The tests that are run should pass without raising MaxTriesExceededException or other exceptions.