New link options and test script

For full documentation for each of the new link options, see the VViki help file in doc/vviki.txt. The options are as follows:

• g:vviki_page_link_syntax
• g:vviki_visual_link_creation
• g:vviki_links_include_ext

The new test suite makes testing new and existing features much, much more convenient. It is interactive (that is to say, not automatic) and is intended to be used to confirm/debug features (as well as catch regressions).

v1.0.0 - Basic functionality complete

I'm calling this release 1.0.0 since I consider VViki to now be feature complete:

• Enter creates/follows page links
• Backspace returns to previous page
• Tab jumps cursor to next link on page
• AsciiDoc link "macro" syntax concealed until cursor enters line

I have been using VViki daily in my personal computing since the first Github commit. I expect to slowly roll out minor versions as I complete wishlist TODO items. There will be patch versions for any bugs, following semantic versioning conventions.