Custom Scan APIs (1/3)

https://commitfest.postgresql.org/action/patch_view?id=1282
http://archives.postgresql.org/message-id/CADyhKSWFY-bfNwrF3zp3e9DvO03na2U4RyCo2uXKUb_vKetXjA@mail.gmail.com
Custom Scan APIs (2/3)

https://commitfest.postgresql.org/action/patch_view?id=1282
http://archives.postgresql.org/message-id/CADyhKSWFY-bfNwrF3zp3e9DvO03na2U4RyCo2uXKUb_vKetXjA@mail.gmail.com
Custom Scan APIs (3/3)

https://commitfest.postgresql.org/action/patch_view?id=1282
http://archives.postgresql.org/message-id/CADyhKSWFY-bfNwrF3zp3e9DvO03na2U4RyCo2uXKUb_vKetXjA@mail.gmail.com