Added a 'Function 7'

[danielfosseliusspot]

I have a case when i need seven futures to combine

[codecov-io]

Codecov Report

Merging #59 into master will not change coverage. The diff coverage is 100%.

@@           Coverage Diff           @@
##             master    #59   +/-   ##
=======================================
  Coverage       100%   100%           
- Complexity       69     73    +4     
=======================================
  Files             6      7    +1     
  Lines           191    208   +17     
  Branches          9      9           
=======================================
+ Hits            191    208   +17

Impacted Files	Coverage Δ	Complexity Δ
...n/java/com/spotify/futures/CompletableFutures.java	100% <100%> (ø)	43 <2> (+2)	:arrow_up:
src/main/java/com/spotify/futures/Function7.java	100% <100%> (ø)	2 <2> (?)

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[danielfosseliusspot]

@mattnworb, @mbruggmann PTAL

[mattnworb]

I don't feel very qualified to review this, but I've added a few other reviewers.

[spkrka]

The change looks good, but I am wondering if it would be better to implement something similar to Futures.join in https://github.com/spotify/futures-extra#joining-multiple-futures instead - that would work for any number of futures to join in a typesafe way.

[danielfosseliusspot]

I have no problems with checking on different solutions, so you mean that in the method combineFutures i would use FuturesExtra.join() instead? The case i have is to extend this method: https://ghe.spotify.net/agglib/agglib-common/blob/master/agglib-taste/src/main/java/com/spotify/taste/clients/TasteClient.java#L85 with two more futures

[danielfosseliusspot]

i was able to solve this in another way