Merge branch '65-binding_model-render_pass_continue' into 'master'

65 binding model test: added missing flags switch: VK_COMMAND_BUFFER_USAGE_RENDER_PASS_CONTINUE_BIT

This fixes issue #65

spec: If vkCmdExecuteCommands is being called within a render pass instance, any given element of pCommandBuffers must have been recorded with the VK_COMMAND_BUFFER_USAGE_RENDER_PASS_CONTINUE_BIT

See merge request !119