TODO

== Auxiliary features
* Methods requests tagging

If algorithm requires some state or property of object, it should be tagged.
Requirements should be checked before each method call (of course, info should
be cached due to computational complexity of algorithms).
Example:

class Polygon

  def convex?
    ...
  end

  def self_intersecting?
    ...
  end

  must_be :convex
  must_not_be :self_intersecting
  def contains_point?(point)
    ... # code, which assumes, that polygon is convex and not self_intersecting
  end

== Algorithms

* Polygon convexity
* Polygons intersection
* Polygon contains given point?
* Rectangular bounds of polygon
* Area of polygon
* Does circle contain given point?
* Do circles intersect?
* Area of circle
* Making a ruby gem