Version 2.0

[antoinelamy]

Complete rewrite of the library bringing a couple of improvements:

• A more Swift API. The version 1.0 is a literal translation of an Objective-C project so some concepts and patterns were improved for a better Swift interoperability.
• Default image ressources doesn't have to be linked with host application anymore. In fact, the images were deleted because they were unnecessary.
• Fine grained control over the effective ranges of clusters and over the number of cluster categories.
• Added customizations on cluster's appearance. It can be configured to a background image or to a solid color like the example (size, background color, border width, font size, font name).

Some additional work needs to be done on the Readme page before it can be merged but I submit it now for review so everyone can take the time to get their head around it and propose changes early in the process.

[Alex293]

Does this improve reusability of clusters (updating count and size) ?