Envato Marketplace

**What does your instant answer do?**
Search products across the Envato marketplace.

**What problem does your instant answer solve (Why is it better than organic links)?**
It's the faster way to find a product you're looking for.

**What is the data source for your instant answer? (Provide a link if possible)**
http://marketplace.envato.com/api/documentation

**Why did you choose this data source?**
It's the only way to fetch Envato's products.

**Are there any other alternative (better) data sources?**
No.

**What are some example queries that trigger this instant answer?**
themeforest responsive modern portfolio

**Which communities will this instant answer be especially useful for? (gamers, book lovers, etc)**
graphic designers, programmers, bloggers, etc.

**Is this instant answer connected to a DuckDuckHack instant answer idea?**
No.

**Which existing instant answers will this one supersede/overlap with?**
None.

**Are you having any problems? Do you need our help with anything?**
No, thank you :)

**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 compatability

    Please let us know which browsers/devices you've tested on:
      - Mac OSX
        [X] Google Chrome   
        [X] Firefox         
        [X] Opera

Would put this outside of the `handle` function because we don't want to concatenate every time the IA is triggered. We only want to do it once (it's cheap, but it's been convention to put constants / immutable variables outside)