pointer-gestures: Correct pluralization, one space, minor vertical whitespace

Adjust double-space after period to be consistent with all content.
Adjust vertical whitespace surrounding first and last protocol tag to
match conventions in this, and other, protocol xml docs.

Signed-off-by: Yong Bakos <ybakos@humanoriented.com>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>