Include dwmipcpp as a library in cmake and config files, so it can be built
automatically. The configuration of dwmicpp was added to match that of i3 and
bspwm to maintain the same cmake workflow and style.
* Use GNUInstallDirs instead of hardcoded paths
This change should be a no-op in the normal case and at the same time make it
easier to customise polybar builds on systems with special needs.
* Avoid creating /usr/share/doc/polybar/polybar/*
* Include GNUInstallDirs for the doc target itself
* cmake: Don't try to set CMAKE_INSTALL_* variables
Since we include GNUInstallDirs all these variables are already set
* cmake: Print install directories in summary
* fix(cmake): Make doc-only work like normal build
This is kind of a dirty hack to force CMAKE_INSTALL_DOCDIR to use
`polybar` as the project name when only polybar-doc is built.
Maybe it is wiser at some point to be able to do a doc only build (and
install) that can be done from the top level project. Then we would also
not need to include GNUInstallDirs here
