go to definition: don't require that cursor is a definition before it's source location is resolved
updated icons for struct and enum
ignore meta key modifiers when cpp completion popup is displaying
guard against null / emptiness in JSON object
Merge pull request #194 from rstudio/bugfix/rnw-completion-null-check

guard against null / emptiness in JSON object
Merge pull request #195 from rstudio/feature/r-autocompletion-tweaks

More R autocompletion additions
rename some cpp definition oriented types
allocate smaller time units to incremental cpp indexing
record both name and parent name
search cpp definitions for go to file/function
don't auto-popup function arguments