CDRIVER-2037 convenient static linking

Whether built with CMake or the Autotools, libbson now installs CMake
config-file packages for bson-1.0 and bson-static-1.0, and pkg-config
files for the same.

Compile and link an example program with all combinations: libbson built
with CMake or the Autotools, using static or dynamic linking, and
finding libbson with the CMake find_package command or with pkg-config.