Problems adding escaped pipes in tables

[notslang]

From @derek-austin in notslang/atom-tidy-markdown#62

Please add an option to disable HTML escapes substitution

Use case for the option:

If you have 'Run on Save' and save this

Command | Description
------- | ------------------------
ls      | list directory contents 
ls | wc | count directory contents
ls \| wc | count directory contents
ls | wc | count directory contents 

you get this

Command | Description
------- | ------------------------
ls      | list directory contents
ls      | wc                       | count directory contents
ls \    | wc                       | count directory contents
ls | wc | count directory contents

if you save it again you get this:

Command | Description
------- | -----------------------
ls      | list directory contents
ls      | wc                      | count directory contents
ls \    | wc                      | count directory contents
ls      | wc                      | count directory contents

If you disable the HTML escape substitution you could use the | hack to render the table.

[notslang]

...and that shouldn't just be an option, that should just be the default behavior. Passing already "cleaned" markdown through tidy-markdown should never result in it being changed.