Update doc.
Support SyncTeX with subdirectory documents.
Add support to Zathura (>= 0.3.1) SyncTeX system.
No longer use R to open the PDF from Rnoweb.
To get a better control of the PDF viewer, use Vim to open the PDF
generated by either Rnoweb or Rmd.
Changes:
  - The option vimrplugin_openpdf_quietly was deprecated.
  - New option: vimrplugin_pdfviewer.
  - The meaning of vimrplugin_synctex was changed.
Warn of possible reasons for problems in SyncTeX.
Add r-plugin/rmd.snippets to list_for_vimball.
Improve SyncTeX support for Zathura.
Make SyncTeX work when 'noautochdir'.
Suggestion to use knitr option cache.lazy=FALSE.
Make SyncTeX work with spaces in path.
Improve help document layout.
Note about knitr limitations regarding SyncTeX.
Use dbus-send to SyncTeX forward Zathura.
Require vimcom 1.0-5.
Add R script with sample code to be indented.
If you want to improve the indent/r.vim script, I suggest that you
check your new algorithm with this sample R code.
Fix minor indent bug.
Fix minor bug in indent/r.vim.
Update r-plugin/indent_test.R.
Add r-plugin/indent_test_noalign.R.
Calculate the value of bb only if necessary.