Reproducible clouds

[cesine]

Added some tests for different use cases of reproducible clouds that i found others had asked for.

• As a user I want to be able to remove words and see roughly the same cloud

in this example the word 'roughly' has been removed but all other words stay put 
upon re-render because
1. the draw function saves color and transform on the word

• As a user I want be able to have every draw of the same text look the same
  • Added pluggable random number generator jasondavies/d3-cloud#1 (comment) be able to reproduce word clouds
  • https://github.com/jasondavies/d3-cloud/pull/1#issuecomment-11984751` able to re-create word clouds would be an extremely useful feature for consistent output on a page
  • Add startPoint option to control where initial words get placed jasondavies/d3-cloud#8 (comment) use the tag cloud as a concrete navigation element for document search and there it is confusing when the tag cloud looks different every time the page is reloaded
  • Replicable cloud jasondavies/d3-cloud#14
  • add a call to allow specification of RNG function jasondavies/d3-cloud#35
  • Add ability to specify random seed value jasondavies/d3-cloud#45 (comment) ensure you have the same layout each time

in this example the same text is drawn the same because 
1. the draw function saves color and transform on the word
2. a random generator is used with the same seed now that we have various PRs requests implemented in 1.1.x 

• As a user I want to be able to save my cloud to a database and re-open it without losing my layout
  • Added pluggable random number generator jasondavies/d3-cloud#1 (comment) being able to save/replay certain word clouds using just the seed number.

in this example a stringified json is used to supply the words and they are drawn the same on every load because 
1. the draw function saves color and transform on the word