Added n-sided prism primitive
Made the cleanup suggested by @ToxicBakery. Also fixed an issue related to terminated cones due to me trying to get fancy with the math and dividing by 0.

Signed-off-by: Jared Woolston <jwoolston@tenkiv.com>
Fixed IllegalArguementException being thrown for sides > 3. Ooops.

Signed-off-by: Jared Woolston <jwoolston@tenkiv.com>
Merge pull request #691 from Tenkiv/NPrism

Added n-sided prism primitive