Suport markdown in table

[majkinetor]

Currently, syntax for editing table is almost like markdown but not quite.

Editing tables in integrated editor is very annoying. I edit the table in vscode and use various Markdown plugins to help with formatting. Then I have to "fix the markdown" so it applies correctly to the pencil table.

This needs to be done:

1. Support starting and ending |
2. Support having table header row
3. Tasks in flavored markdown use [x] instead and [*]`
4. Allow empty lines at the end

As a side note, it would be even better to support Markdown in text areas.