Allow ActiveRecordViews to load ERB files

Partially fixes: #6 

First it checks for a matching `.sql` file before looking for a `.erb`

Could potentially use some work to make partial rendering a thing without having to go:

``` erb
<%= File.read '/path/to/_partial.erb' %>
```
Okay. I see the block is still required. Perhaps just this bit then:

```ruby
if sql_path.end_with?('.erb')
          ERB.new(File.read(sql_path)).result
        else
          File.read(sql_path)
        end
```