Custom Metrics

![getinsertpic.com](http://media4.giphy.com/media/JbBGymTFL7AgU/200.gif)

## Problem

We want to plug some custom metrics about the broker into AWS CloudWatch.

## Solution

Use the new [Alephant-Logger](https://github.com/BBC-News/alephant-logger) `metric` interface.

> Note: Alephant-Logger has been implemented in a way that means if the consumer of Alephant-Renderer doesn't have a need for recording CloudWatch metrics then they simply don't wrap the Logger in the provided Decorator class (meaning any calls to `metric` become a no-op)
This is causing an error as the exception is expected in the specs but you're catching it here now rather than letting it bubble up.

Might make more sense to be something like:

```ruby
if File.directory?(path)
  @base_path = path
else
  logger.metric({:name => "RenderViewMapperInvalidPath", :unit => "Count", :value => 1})
  raise "Invalid path: '#{path}'"
end
```