prompt for installation of rmarkdown package
resolve path for package archives path
update rmarkdown whenever SHA1 doesn't match
add support for format-specific R Markdown option variants
be more selective about rmarkdown updating
add R Markdown format definition for Word
add rmarkdown package to notice
Merge remote-tracking branch 'origin/master' into feature/new-rmarkdown-dialog

Conflicts:
	src/cpp/session/modules/SessionRMarkdown.R
	src/gwt/src/org/rstudio/studio/client/rmarkdown/model/RMarkdownServerOperations.java
	src/gwt/src/org/rstudio/studio/client/workbench/views/source/editors/text/TextEditingTargetRMarkdownHelper.java