Added guidelines for clear Markdown formatting and language requirements
Update CONTRIBUTING.md

Fixed a minor grammar mistake and changed "will be closed" regarding posting in English to be slightly more friendly.
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
Merge branch 'master' into scenegraph