Interval Skip List 

This data structure maps intervals to values and allows you to find all
intervals that contain an index in O(ln(n)), where n is the number of
intervals stored. This implementation is based on the paper
The Interval Skip List by
Eric N. Hanson.

Basic Usage Example

``coffee
IntervalSkipList = require 'interval-skip-list'
list = new IntervalSkipList

list.insert('a', 2, 7)
list.insert('b', 1, 5)
list.insert('c', 8, 8)

list.findContaining(1) # => ['b']
list.findContaining(2) # => ['b', 'a']
list.findContaining(8) # => ['c']

list.remove('b')

list.findContaining(2) # => ['a']
`

API

* ::insert(label, startIndex, endIndex)
Adds an interval with the given unique label to the list.

* ::remove(label)
Removes the interval with the given unique label from the list.

* ::update(label, startIndex, endIndex)
Inserts or updates the interval corresponding to the given unique label.
Unlike ::insert, this method allows you to specify a label that's already
been inserted in the list.

* ::findContaining(indices...)
Returns the labels of all intervals containing the given indices.

* ::findIntersecting(indices...)
Returns the labels of all intervals intersecting the given set of indices.
Unlike ::findContaining, this method does not require that the intervals
contain all the given indices.

* ::findStartingAt(index)
Returns the labels of all intervals starting at the given index.

* ::findEndingAt(index)
Returns the labels of all intervals ending at the given index.

* ::findStartingIn(startIndex, endIndex)
Returns the labels of all intervals starting within the interval described by
the given start and end indices.

* ::findEndingIn(startIndex, endIndex)
Returns the labels of all intervals ending within the interval described by
the given start and end indices.

Using a Custom Comparator

You can also supply a custom comparator function with corresponding min and max
index values. The following example uses arrays expressing coordinate pairs
instead of the default numeric values:

`coffee
list = new IntervalSkipList
minIndex: [-Infinity, -Infinity]
maxIndex: [Infinity, Infinity]
compare: (a, b) ->
if a[0] < b[0]
-1
else if a[0] > b[0]
1
else
if a[1] < b[1]
-1
else if a[1] > b[1]
1
else
0

list.insert("a", [1, 2], [3, 4])
list.insert("b", [2, 1], [3, 10])
list.findContaining([1, Infinity]) # => ["a"]
list.findContaining([2, 20]) # => ["a", "b"]
``