Use have_library method in mkmf library to detect openbabel library
BSD sed workaround
Read output file extension from RbConfig::CONFIG["DLEXT"]
Generate Makefile with extconf.rb
Merge pull request #2 from ktns/macosx

Installation problem on MacOSX
Use Kernel.system instead of `command`
Use running ruby executable to compile the binding
-Wl,-flat_namespace workaround
Define OpenBabel::VERSION,GEMVERSION
Use OpenBabel::VERISON to build gem
Loadpath workaround