fix(iterator): Restore building on GCC 7.1

This resolves errors about using an incomplete class in generic::list's
begin() and end() functions as well as class template specializations
occurring outside of namespace scope.

fix(cmake): Remove X11

fix(cmake): Use `target_compile_options` for library flags

Refs https://github.com/jaagr/polybar.git#308

fix(event): Safety check for dynamic_cast

fix: Patch xkb dispatcher

fix(cmake): Include xcb sync and composite if specified

fix(cmake): Require xcb-util-image

Move header files to namespace subdir

Include dir symlink

Include dir symlink