All #ifndef guards on headers have been removed, I think,
in favor of #pragma once
Headers are now included as `#include "filename"` if the included file
resides in the same directory as the file including it, or any
subdirectory therein. Otherwise they are included as
`#include <project/top/dir/relative/path/filename>`
The above does not include system/os headers.
* add conf.d directory for config overrides
* refactor llarp::Config
* add explicit constructor with datadir as parameter
* have all config files be passed as std::optional
* make Config::LoadDefault private and use std::optional in Config::Load to remove ambiguity
* update rest of codebase to reflect above changes
* fix pybind
* rename bootstrap config skipBootstrap to seednode as it's more descriptive
* make seednode configurable
* make pybind layer compile
* make pybind layer run
