Version 3.0.0

0. No behavioral changes to command logic.
1. Tab option 'line_number_at_window_top'
   renamed => 'line_number_at_netrw_window_top'

2. Add configurable build of command aliases :T, :V, :H, and :TF
   for :Tabwins* commands.  An alias is NOT BUILT IF an existing
   command has the same name.  See ""Configuration"/*TabwinsConfiguration*
   in tabwins.txt.

3. All defaults to Fill_tab() are now user-configurable global vars.

4. Most functions converted to vimscript ':s' scope -- the
   Explore_*() functions and Fill_tab() are the exceptions.

5. Demo tabs are now :Tabwins* commands rather than functions.
6. Remove the :Ot* abbreviated commands for the demo tabs.
7. tabwins.txt: Add example builder command, & various improvements.
8. Comments in code cleaned up.
Version 3.1.0

1. For fill_specs that are files, put line #1 at window top.
2. tabwins.txt: correct Fill_tab() key 'dir_cmd_name'     to 'explore_cmd_name'
3. tabwins.txt: correct 'tabwins_dir_reader_name_default' to 'tabwins_explore_cmd_name_default'
4. tabwins.txt: various improvements.