Requires WP and Requires PHP

[ePascalC]

Add logic as per https://core.trac.wordpress.org/ticket/46938

[ePascalC]

'Requires WP' is not a valid tag, should be 'Requires at least' 'Requires PHP' and 'Requires at least' should go in the main plugin file

Checks:

• If 'Requires WP' is found, warning that it should be 'Requires at least'
• If they are in readme AND in main plugin file, recomendation to remove from readme (the ones in readme are not taken into account since WP 5.3)
• If they are only in readme, warning to move them to plugin file (currently they are still taken into account, but deprecated since WP 5.3)

[ePascalC]

https://github.com/bbpress/bbPress/pull/2/files