XE.com Currency Spice

**What does your instant answer do?**
- Provides multiple currency exchange rates using XE.com data

**What problem does your instant answer solve (Why is it better than organic links)?**
- Usually if a person is searching a currency, they are interested in seeing the relative currency worth.

**What is the data source for your instant answer? (Provide a link if possible)**
- http://www.xe.com

**Why did you choose this data source?**
- Best currency exchange rates on Internet.  :)

**Are there any other alternative (better) data sources?**

**What are some example queries that trigger this instant answer?**
- usd
- 10 usd cad

**Which communities will this instant answer be especially useful for? (gamers, book lovers, etc)**
- travel, finance

**Is this instant answer connected to a DuckDuckHack [instant answer idea](https://duck.co/ideas)?**
- no

**Which existing instant answers will this one supersede/overlap with?**
- wolfram alpha

**Are you having any problems? Do you need our help with anything?**
- no

**\*\*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
[X] Wrote test file and added to t/ directory
[X] Verified that instant answer adheres to design guidelines(https://github.com/duckduckgo/duckduckgo-documentation/blob/master/duckduckhack/styleguides/design_styleguide.md)
[X] Tested cross-browser compatibility

    Please let us know which browsers/devices you've tested on:
    - Windows 8
        [X] Google Chrome   
        [X] Firefox         
        [X] Opera           
        [X] IE 10           

    - Windows 7
        [X] Google Chrome   
        [X] Firefox         
        [X] Opera           
        [X] IE 8            
        [X] IE 9            
        [X] IE 10           

    - Windows XP
        [] IE 7            
        [X] IE 8            

    - Mac OSX
        [X] Google Chrome   
        [X] Firefox         
        [X] Opera           
        [X] Safari          

    - iOS (iPhone)
        [X] Safari Mobile   
        [X] Google Chrome   
        [] Opera           

    - iOS (iPad)
        [X] Safari Mobile   
        [X] Google Chrome   
        [] Opera            

    - Android
        [X] Firefox         
        [X] Native Browser  
        [X] Google Chrome   
        [] Opera
```

![2300_usd_in_cad_at_duckduckgo](https://cloud.githubusercontent.com/assets/116121/4276439/3661ba26-3d05-11e4-86e8-143e8794a390.png)

![image](https://cloud.githubusercontent.com/assets/116121/4276417/0a10a144-3d05-11e4-8d01-0ca35709d135.png)

The parameter to the `Spice.failed` should be the ID, so we can just call `Spice.failed("currency")`