* add installation support for pkg-config dependency detection
pkg-config is a buildsystem-agnostic alternative to
`pybind11Config.cmake` that can be used from build systems other than
cmake.
Fixes#230
* tests: add test for pkg config
Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>
Co-authored-by: Henry Schreiner <henryschreineriii@gmail.com>
Eli Schwartz