Added a new Goodie instant answer which converts a word from plural to singular

**What does your instant answer do?**
It converts a word from plural form to singular

**What problem does your instant answer solve (Why is it better than organic links)?**
For a quick answer, it is much faster than navigating to organic links and reading through paragraphs of text for one word.

**What is the data source for your instant answer? (Provide a link if possible)**
None. I am using a CPAN module to do the transformation

**Why did you choose this data source?**
N/A

**Are there any other alternative (better) data sources?**
N/A

**What are some example queries that trigger this instant answer?**
singular tablets

**Which communities will this instant answer be especially useful for? (gamers, book lovers, etc)**
ESL users and primary school students

**Is this instant answer connected to a DuckDuckHack [instant answer idea](https://duck.co/ideas)?**
Not that I am aware of.

**Which existing instant answers will this one supercede/overlap with?**
I did not find any other Goodie instant answer which overlaps

**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.
![image](https://cloud.githubusercontent.com/assets/4030646/3794464/77b3bfe8-1bad-11e4-98f3-b84450d1d6bf.png)



## 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://duck.co/duckduckhack/design_styleguide)
[X] Verified that instant answer adheres to code styleguide (https://duck.co/duckduckhack/code_styleguide)
[] 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
```
I'm a little weary of using "single" as a trigger word, I feel like it would be too broad, I think we can improve the triggering by using phrases (e.g. "singular form of", "singular of") or using phrases like "singular form" and then us a regex in your handle to ensure the query shows some intent to trigger this IA. 

For example "singular of geese" wouldn't trigger this IA currently and "single mom" would (though it might not return a result)