Feature: [markdown-mode] - Add functionality to work with tables

[Encryptoid]

It would be good if there was some ways to work with tables in markdown-mode.

Features:

• Align table contents
• Add new row/column
• Remove row/column
• Add |------| line below header line
• Move cell up/down/left/right

This would conform to common markdown standards: https://www.codecademy.com/resources/docs/markdown/tables

Could be a good task if someones likes markdown/text processing.