Add find_topics function

[ledell]

Issue: #44

Here's how it works:

> topics <- find_topics(text = "R-Ladies", api_key = api_key)
Downloading 2 record(s)...
> topics
# A tibble: 2 x 7
       id name          urlkey         member_count description                       group_count resource
    <int> <chr>         <chr>                 <int> <chr>                                   <int> <list>  
1 1513883 R-Ladies      r-ladies              40839 Find out what's happening in R-L…         141 <list […
2 1387242 WHERE R U HE… where-r-u-hea…            0 Find out what's happening in WHE…           0 <list […

Once you see the topic id, you can use it find all groups of that specific topic:

> groups <- find_groups(topic_id = 1513883, api_key = api_key)
Downloading 141 record(s)...

[ledell]

Hey @LucyMcGowan do you have any comments on this PR?

[ledell]

@hfrick Do you mind taking a quick review of this?

[hfrick]

sure! (it'll be next week though)

[drmowinckels]

I've not added test etc for the new functions in this PR, but have gone through and resolved conflicts with current master @maelle and @ledell

But forgot to run checks. Will get the new funcs adapted to the new api.

[drmowinckels]

I didnt fix tests, sorry, just have not have time to sit down with vcr and understand how it works. But I have made sure the PR no longer has conflicts with master, and that is generally fits with the updates lately. I also collected the two find-functions into a single file with common rd.

[benubah]

With the new GraphQL API, this PR should be obselete?