Add llpp.19

Blurb:

llpp a graphical PDF viewer which aims to superficially resemble
less(1)

Changes:

* Optional fontconfig support
* Reorganized/improved help screen (Michael Asnes)
* History mode
    Somewhat breaking change, full paths are now stored not just file
    names. This mode is entered by default when llpp is invoked without
    a path to the document to be viewed.
* Bugfixes
Why is this needed? I can't find any other mention of install.sh in this merge-request.