Add NewSliceStringerAllGoPackages (mode 6) experiment; begin VfsListingWidget.

VfsListingWidget will replace FolderListingWidget.
Use markdown_http.MarkdownOptionsHandlerFunc instead of static table of contents.
Print time to display first frame (in addition to loading time).
Make VfsListingWidget use a vfs.FileSystem for its operations.
Add VfsListing0Widget (copy of VfsListingWidget at start) for comparison.
Update to Go 1.4 compatible bypass package.
Add options, support single/optional section to FilterableSelecterWidget.
Minor code refactor.
Replace VfsListingPureWidget inner list implementation with FilterableSelecterWidget.
Switch from FolderListingWidget to VfsListingWidget in mode 1.

Add support for left/right arrow keys in VfsListingWidget.
Filter folderListing to show only .go files.
Remove FolderListingWidget, VfsListing0Widget.

They are now obsoleted by the more general and code-reusing
VfsListingWidget.
Remove file listing from /status/ page.
Use "path" package for vfs, not "filepath".

There's still more cleaning up to be done.
Add Cmd+O select package listing and enter/esc focus editor shortcuts.
Update moved import path.
Select func name only, center if offscreen.
Make WholeWordHighlighter highlight whole words only.

Previously, it activated when a whole word was selected, but it
highlighted non-whole words occurrences. Now it only highlights whole
words.
Add backend support for whole word only find results.
Room for simpler way to calculate isWholeWord for arbitrary word
positions; can be optimized later.
Add whole word checkbox to Find Panel.
Move resources into ./data/ subfolder.