Deprecate runVis in favor of runShiny

As [discussed before](https://github.com/cpsievert/LDAvis/issues/6), `runVis` was not a great implementation since it assumed certain object existed in the workspace. These changes will deprecate `runVis` in favor of `runShiny` which allows one to pass objects to the shiny app explicitly as well as easily [embed the shiny app](http://rmarkdown.rstudio.com/authoring_embedded_shiny.html) into R Markdown documents. This pull request will close issue [#11](https://github.com/cpsievert/LDAvis/issues/11).