add render_delayed wrapper to delay evaluation to runtime
better safeguards from early evaluation
add documentation and exports
don't leave the Shiny document loading symbol up after an error
don't depend on S3 method for delayed output
Merge pull request #106 from rstudio/shiny-delayed-rendering

Delayed rendering for Shiny documents
bump version
Merge remote-tracking branch 'origin/master' into htmltools-refactor