Allow multiple rows inside single table

[getglad]

Reduces impact of unintended spacing created between tables when message is forwarded.

Partially resolves foundation/foundation-emails#308
And: http://stackoverflow.com/questions/36320051/outlook-adding-paragraph-after-every-table

Use case would work like this:

  <row2>
    <innerrow class="descriptive_table_header">
      <columns2 large="2">
        Product Name
      </columns2>
      <columns2 large="3">
        Price
      </columns2>
      <columns2 large="4">
        Shipping
      </columns2>
      <columns2 large="3">
        Date
      </columns2>
    </innerrow>
    <innerrow class="descriptive_fields">
      <columns2 large="2">
        Product A
      </columns2>
      <columns2 large="3">
        $20.00
      </columns2>
      <columns2 large="4">
        2 days
      </columns2>
      <columns2 large="3">
        Get it by Friday
      </columns2>
    </innerrow>
    <innerrow class="descriptive_fields">
      <columns2 large="2">
        Product B
      </columns2>
      <columns2 large="3">
        $50.00
      </columns2>
      <columns2 large="4">
        3 days
      </columns2>
      <columns2 large="3">
        Get it by Saturday
      </columns2>
    </innerrow>
  </row2>

Happy to answer any questions

[rafibomb]

Thanks for the PR! Can you describe how someone would use this new tag? Is it used in place of the standard <column>?

[rafibomb]

We think this might be a specific use case that can be a separate plugin or extension to Inky. We'd like to get extensions like this to be easily created with Inky like proposed here: #30

Next step is to make adding Inky plugins a simple process and storing these "add-ons" in an easy to find place.

[getglad]

Sure - if the plugins become an organized initiative let me know if I can help