Blender Git Loki

Use function pointer; remove redundant variables.

Export packed image file names, not paths.

Use const; move constructors to implementation file.

Merge branch 'master' into soc-2020-io-performance

Cleanup: renaming & comments.

Fix several material import bugs, remove wrong assert.

Images were not being loaded since the parent directory was
missing in the path. So add it in tex_map_XX.

Merge branch 'master' into soc-2020-io-performance

Fix loose edge export & import, and offsets.

Fix vertex offsets for MEdges and MLoops.

Catch out of range exceptions for stoi/stof.

Add vertex offset due to Curves' vertices also.

Fix new Geometry creation with empty initial object.

Use const& instead of pointers in Mesh class.

Correct geometry creation code with Curves.

Also make `Geometry` and `GlobalVertices` members of
`CurveFromGeometry` as `const &` to match with
`MeshFromGeometry`.

Merge branch 'master' into soc-2020-io-performance

Use FILE_MAX instead of PATH_MAX

Also, allow more vertices data points to be in int
strings.

Accept 3D UV vertex coordinates

The third one is still discarded.

Create new Geometry instance at the start.

Since the following is a valid OBJ file, a new `Geometry` instance
is always required.

```
v 1.0 2.0
```

Move index offset from parsing to Object creation

The only place where the information needed about how many vertices
have been occupied by other objects is `mloop->v` since `v` has to
be in the range from zero to total vertices _in a_ mesh.

All other indices (edge, UV, normal) work best when they're parsed
the way they're written and the corresponding data from the global
list is read directly.

So instead of modifying every index just to keep `mloop->v` happy,
use a `Map<int, int>` for storing vertex indices. This reduces chances
of error greatly and avoid "indices to indices to coordinates".

`Vector` would've been very slow it being unsorted & lookups being done
for _all_ `mloop`s. `Map` gives no drop in performance.

UV vertices from `Geometry` have been removed since `FaceCorner`s store
a direct index indexing into the Global list of UV coordinates.

Fix wrong material exporter assert added recently.

Since Alpha in RGBA is not written to the MTL file, callers
use array of length 3.