Add CanIUse module

**What does your instant answer do?**
Looks up browser feature compatibility from CanIUse.

**What problem does your instant answer solve (Why is it better than organic links)?**
It lets you quickly see if a feature is supported in major browsers.

**What is the data source for your instant answer? (Provide a link if possible)**
http://caniuse.com/
https://raw.githubusercontent.com/Fyrd/caniuse/master/fulldata-json/data-2.0.json

**Why did you choose this data source?**
It's the best that I know of.

**Are there any other alternative (better) data sources?**
No

**What are some example queries that trigger this instant answer?**
caniuse contenteditable
caniuse indexeddb

**Which communities will this instant answer be especially useful for? (gamers, book lovers, etc)**
Web developers & designers.

**Is this instant answer connected to a DuckDuckHack [instant answer idea](https://duck.co/ideas)?**
https://duck.co/ideas/idea/615/when-can-i-use-caniuse-com

**Which existing instant answers will this one supercede/overlap with?**
None that I know of.

**Are you having any problems? Do you need our help with anything?**
The dev env was very easy to set up (kudos!), but I wasn't sure how to test FatHead answers.

How does the meta file in `lib/DDG/Fathead/CanIUse.pm` map to the files in `share/caniuse/`?


**\*\*Note:** Please attach a screenshot for new instant answer pull requests, and for pull requests which modify the look/design of existing instant answers.

## Checklist
Please place an 'X' where appropriate.

```
[X] Added metadata and attribution information
[] Wrote test file and added to t/ directory
[] Verified that instant answer adheres to design guidelines(https://github.com/duckduckgo/duckduckgo-documentation/blob/master/duckduckhack/styleguides/design_styleguide.md)
[] Tested cross-browser compatibility

    Please let us know which browsers/devices you've tested on:
    - Windows 8
        [] Google Chrome   
        [] Firefox         
        [] Opera           
        [] IE 10           

    - Windows 7
        [] Google Chrome   
        [] Firefox         
        [] Opera           
        [] IE 8            
        [] IE 9            
        [] IE 10           

    - Windows XP
        [] IE 7            
        [] IE 8            

    - Mac OSX
        [] Google Chrome   
        [] Firefox         
        [] Opera           
        [] Safari          

    - iOS (iPhone)
        [] Safari Mobile   
        [] Google Chrome   
        [] Opera           

    - iOS (iPad)
        [] Safari Mobile   
        [] Google Chrome   
        [] Opera            

    - Android
        [] Firefox         
        [] Native Browser  
        [] Google Chrome   
        [] Opera
```

Hey @jdorweiler, just a heads up that the query `caniuse css-gradient` doesn't work for me. The other example queries do work though.