Implement math#abs
Implement math#acos
Implement math#asin
Make acos and asin tests correct

a < b < c syntax doesn't evaluate correctly in JS. Better remember that!
Implement math#atan
Implement math#atan2
Implement math#ceil
Implement math#cos
Make range end work with zero
Make math#between consistent with math#clamp
Tidy up tests
Implement math#exp
Implement math#floor