Implement basic module opening/closing functionality
Implement basic module opening/closing functionality

This patch adds:

- Finding .so files in the usual system-wide libraries, or using relative or
  absolute paths.
- Opening .so files with libdwarf/libelf.
- Wrapping libdwarf handles using Lua userdata.

aperezdc/lua-eol,aperezdc/eris,aperezdc/lua-eol,aperezdc/eris