Issue with makrdown file path stored in post meta

As the complete path of markdown files to be imported gets stored in post meta. It causes an issue if:

1. The absolute path to the plugin folder then changes.
2. Name of the plugin changes.

Both of these issue happened in our case.

Had to run the following search-replace commands to fix this:

```bash
wp search-replace '/var/www/htdocs/wp-content/plugins/ee-markdown-importer/' '/var/www/htdocs/current/wp-content/plugins/wp-ee-docs-command/' --url=

wp search-replace '/var/www/htdocs/wp-content/plugins/wp-ee-docs-command/' '/var/www/htdocs/current/wp-content/plugins/wp-ee-docs-command/' --url=
```