This replaces the generation of man pages on project setup
by a on-demand generation via asciidoctor.
An exception are the man pages for the commands `day`, `month`, and `week`
which are simply redirects to the man page `timew-chart.1`. Those are now
static files in the Timewarrior repository.
A CMake find module to detect asciidoctor was added.
If asciidoctor is found, the targets `doc`, `man1`, and `man7` are created.
Those targets are also added to the default build target.
If asciidoctor is not available, the target `doc` is available, but it only
emits a message to install asciidoctor first.
Signed-off-by: Thomas Lauf <thomas.lauf@tngtech.com>
