#1173 [SciTE] Hide buffer numbers in tab

[desto]

Added an option to hide the buffer number from the tabs.
tabbar.hide.index=1
Any number != 0 works.

The numbers will still be shown in the Buffers submenu, and Alt+<index> shortcuts still work on both GTK+ and Windows.</index>

[Neil Hodgson]

Committed as [5a6511]. Changed the documentation to be more similar to other properties.