Added geometry formula shower / calculator Goodie

**What does your instant answer do?**
This goodie shows geometric formulas (e.g. circle area) or calculates them if sizes are specified.

**What is the data source for your instant answer? (Provide a link if possible)**
The german "Tafelwerk", because it is a good formulary

**What are some example queries that trigger this instant answer?**
formula circle area
for more: see test file

**Is this instant answer connected to a DuckDuckHack [instant answer idea](https://duck.co/ideas)?**
Yes, https://duck.co/ideas/idea/1053/geometry-calculator.

**Which existing instant answers will this one supercede/overlap with?**
Not known yet

**Are you having any problems? Do you need our help with anything?**
Not yet

- [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 *with support tables*; in brackets the feature which is used and has the lowest support for this browser
 - IE from version 9 (SVG)
 - Firefox from version 6 (data-*)
 - Chrome from version 7 (data-*)
 - Safari from version 5 (data-*)
 - Opera from version 11 (data-*)
- [x] Tested live only on Linux 64-bit, Firefox
The `while`, `if` convention seems unnecessary? Why not just use `$_` to access the hash instead of iterating until the current key matches the one we already have?

IMO the approach codepath to get to the result that was request is a little confusing.

The way I would approach this is to first take our raw query and pull our the term's we know we need, such as the requested "formulas" being one or more of (circumference, area, volume, ...).

Once we have that we want to know what were getting these for, it should be one of (cube, triangle, sphere, ...). At this point we can figure out if they're also requested something that doesn't exist (e.g. "volume" of a "circle"), it's unlikely, 
but we should probably bail at this point.

Now that we know what formulas we want, and for what shape, we can grab exactly those from our hash and produce a result

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Again that's the way I would approach this and I think that method should make the code more straightforward and a little easier to understand. Perhaps I'm just not understandign your thinking/approach. Care to explain?