Words goodie

## Introduction

Hi! This PR adds a new goodie, "Words".

**What does your Instant Answer do?**

Gives a list of words, optionally matching a few criteria.

**What problem does your Instant Answer solve (Why is it better than organic links)?**

It's a lot more convenient and flexible than going through the search results and repeating the query on each site.

**What is the data source for your Instant Answer? (Provide a link if possible)**

The Enhanced North American Benchmark LExicon Updated Millennial Edition, AKA Enable2K, released in the Public Domain. The [original source](http://personal.riverusers.com/~thegrendel/)  seems to be down but there are plenty of copies around, usually named "enable2k.zip", ["enable2k.txt"](http://www.morewords.com/enable2k.txt) or ["WORD.LST"](http://www.cs.duke.edu/csed/tapestry/data/yawl/). 

**Why did you choose this data source?**

Quoting the data source itself: "[...] is the most thoroughly researched, and therefore the most authoritative word list and reference available for Scrabble players [...] has become something of a de facto standard for electronic word lists used by word gamers. It has been adopted by developers and programmers for interactive on-line word game servers and word construction (anagramming) software."

Also, it's free (Public Domain).

**Are there any other alternative (better) data sources?**

None that I could find.

**What are some example queries that trigger this Instant Answer?**

* words starting with duck
* 9-letter words like cro*rd
* 20 words
* random words with 4 letters
* 5 6-letter words ending in ay
* words like cro----rd

**Which communities will this Instant Answer be especially useful for? (gamers, book lovers, etc)**

Word games (Scrabble, crosswords,etc) players.

**Is this Instant Answer connected to a DuckDuckHack [Instant Answer idea](https://duck.co/ideas)?**

Yes, I found this instant answer idea [here](https://duck.co/ideas/idea/448/wildcard-word-lookup-for-scrabble-ish-games), waiting for a developer.

**Which existing Instant Answers will this one supercede/overlap with?**

None.

**Are you having any problems? Do you need our help with anything?**

No problems yet. It's the first time I'm writing Perl though, so I'd appreciate a look for mistakes and inefficiencies.

**Where did you hear about DuckDuckHack? (For first time contributors)**

IIRC, on Hacker News.

**What does the Instant Answer look like? (Provide a screenshot for new or updated Instant Answers)**

![words-screenshot](https://cloud.githubusercontent.com/assets/311595/5328628/42b86952-7d90-11e4-8602-5256e267c354.png)

## Checklist
Please place an 'X' where appropriate.

```
[X] Added metadata and attribution information (https://duck.co/duckduckhack/metadata)
[X] Wrote test file and added to t/ directory (https://duck.co/duckduckhack/goodie_tests)
[] 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
```

Hmm I don't see the advantage of treating 1 differently with respect to `@a` here; if you abandon this then this section could be made smaller with something like:
```perl
my $t = "word";
$t .= "s" unless $word_count == 1;
push @a, $word_count unless $word_count == 0;
```