fix description of area()

[donbright]

that appears to be the wedge product, aka area of parallelogram, not triangle. it is twice the area of the triangle. example with points 0,0. 4,0. 4,3. area() = 12, triangle area = 6. thx

[mourner]

"Parallelogram" would probably be confusing here. In this case we're only interested in the sign so it doesn't matter if it's signed; we could just add a comment that it's double the signed area.

[mrgreywater]

To be honest, I also stumbled upon this, and came to the conclusion of @mourner, but maybe it would make sense to rename both the area and signedArea function to something like doubleArea and doubleSignedArea respectively to indicate their result is twice as large.

[mourner]

Another common pattern is to name the function orient.

[donbright]

attempt to fit to issue discussion

[donbright]

added comment it is twice signed area. thx.
this is a math function which has many different names depending on what branch of math the reader has studied.

[donbright]

oops, i deleted my repo on accident. closing since it cannot be merged.