lisp/strokes.el: Fix typos.

lisp/strokes.el: Fix typos.

(strokes-xpm-header, strokes-rate-stroke): Fix typos.
(strokes-character, strokes-get-grid-position, strokes-list-strokes):
Remove superfluous backslashes.
(strokes-last-stroke, strokes-global-map, strokes-mode):
Reflow docstrings.
(strokes-xpm-for-stroke, strokes-xpm-to-compressed-string)
(strokes-xpm-for-compressed-string): Use quotes with buffer name.
(strokes-distance-squared, strokes-global-set-stroke)
(strokes-global-set-stroke-string): Doc fixes.
(strokes-help): Fix typos; reflow docstring.