Remove mathn

[olbrich]

This experimental branch removes the requirement for mathn.

fixes #153, #139, #134, #106, #87, #73, #59, #57, #56, #17

[rposborne]

This is fantastic work, thank you for all your hard effort on this gem.

[kreintjes]

Also fixed #124 right?

Great work, but I think it should have been released in a Major version, since it could break all kinds of calculations. People might have gotten used to integer divisions leading to rationals (1/3 => (1/3)) instead of integers (1/3 => 0).