Nomenclature (for Pie/Donut charts)

[tiraeth]

I am coming with a proposal of fixing nomenclature (for Pie and Donut charts). Right now, in internal functions, Morris.js is using segment while it should use sector.

In geometry the "pizza" slice is called "sector" while "segment" is just a slice made by chord.

I think this Issue is a good start point for checking and fixing all namings in Morris.js (for example, when this is solved we can provide an option called minSectorAngle which is related to #92).