Move vignettes to 'vignettes' directory
Update version and requirements
Remove condition for R 2.13.0; import methods in NAMESPACE
Fix connection leak when requested object file does not exist on disk

* first create connection
* then open it for reading (potentially resulting in error condition)
* always close it (destroying connection) before erring out
Revert "gsub with useBytes = FALSE is very slow"

This reverts commit 301d2c2a5eb7e02a8b9093c81364eba027d0eb5b.
Merge branch 'master' into next

* master:
  Fix connection leak when requested object file does not exist on disk
  Remove condition for R 2.13.0; import methods in NAMESPACE
  Update version and requirements
  Move vignettes to 'vignettes' directory