vppapigen:  update markdown documentation
vppapigen:  update markdown documentation

- Add newly added typedefs.
- Update string examples.

Change-Id: I1e7ee7cbf5901ba97302472521bf1f42a14765ea
Type: docs
Signed-off-by: Paul Vinciguerra <b92f79aabe4c9c18085c7347110a52af0898a0ef@vinciconsulting.com>

chrisy/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp,FDio/vpp,chrisy/vpp