Trigger showing when point is in the "periphery" of a line or just

Trigger showing when point is in the "periphery" of a line or just
inside a paren.
paren.el (show-paren-style, show-paren-delay)
(show-paren-priority, show-paren-ring-bell-on-mismatch): Remove
superfluous :group specifications.
(show-paren-when-point-inside-paren)
(show-paren-when-point-in-periphery): New customizable variables.
(show-paren-highlight-openparen): Make into a defcustom.
(show-paren--unescaped-p, show-paren--categorize-paren)
(show-paren--locate-near-paren): New defuns.
(show-paren--default): Refaactor and trigger on more paren
positions.
(show-paren-function): Small consequential changes.