no-vector 2d web::display
more de-vectorizing
added display doc about drawing origin
Display#image[_cropped] -> #draw_image[_cropped]
minor tweaks
removed vector
vec2
Vec2 #direction #distance_to #direction_to
fixed Vec2 #length & #distance_to, #equals? -> #equal?
Vec2 & misc docs
vec2 tests
vec2 benchmarks
Merge branch 'no-vector'

Conflicts:
	lib/yeah/_platform/display.rb
	opal/yeah/web/display.opal