mesh_t based ruby bindings

This PR will update the ruby bindings for the `csg` gem to be based on the new `mesh_t` type from #49 

This will also bump the gem version to `0.1.0` because of the API shuffling I'm doing.

## Tasks

  * [x] Wrap `mesh_t` into `CSG::Native`
  * [x] Wrap `mesh_read_file` to return a `CSG::Native`
  * [x] Update `CSG::Solid` to be `mesh_t` backed instead of `stl_object`
  * [x] Add `to_bsp` to the `mesh_t` prototype returning a new BSP tree
  * [x] Tests for `mesh_t->to_bsp`
  * [x] `bsp_to_mesh` helper to not deal with CPP generated calls from ruby
  * [x] Tests for `bsp_to_mesh` 
  * [x] Update the FFI binding to include the new method
  * [x] FFI wrapper to construct BSP-backed meshes in ruby
  * [x] Do everything as a mesh in the ruby wrapper
  * [x] Map appropriate methods for I/O and operations

## Maybe this also?

  * [x] Remove the `stl_object` from being exported to ruby?