Blender Git Loki

Rename exportable_meshes to exportable_as_mesh

This change is to make it more clear that this is not a list of
Blender meshes, but objects that are being exported in Mesh form.
Same for NURBS curve.

Refactor: Conform to style guide, add documentation.

Rename classes OBJImporter > OBJParser, OBJParentCollection >
OBJmportCollection.

Move OBJRawObject items to private access & use getters. Parser class
is set to its friend since it edits the Raw object heavily.

Break OBJMeshFromRaw and OBJCurveFromRaw into smaller functions with
one responsibility.

Add comments wherever required.

Use int instead of uint.

Remove typedef, use Span.

Set active NURBS of a curve; set object group.

Correction for `CU_NURB_ENDPOINT` being a valid `flagu` value , not
`flag`.

Cleanup: fix grammar in comments.

Fix build errors: avoid `uint` with Vector size() function.

https://wiki.blender.org/wiki/Style_Guide/C_Cpp#Integer_Types

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

Support NURBS curve import & minimal groups support.

There's a problem though: the curve's vertices appear in edit mode
just fine, but the black line doesn't appear in object mode. But the code
so far should've been committed.

Also, some semantics have been made consistent which needed mesh
related functions/ members to be edited:
- `add_object_to_parent` for mesh is now similar to that of curves.
- `OB_MESH` is the default type of a raw object.

`copy_string_to_int` is also added to support multiple `int` values.

Cleanup: Remove unused functions and headers.

Explicitly specify empty string.

Refactor: move functions out of Importer class

It got left out of the last commit.

Refactor: move functions out of Importer class

No functional change

Move vertex (and UV vertex) list outside OBJRawObject

Since an OBJ file may contain data like [1], the vertex coordinates
list should be detached from any `OBJRawObject`. So every raw object
keeps track of its vertices by indexing into the global list of coordinates.

[1]
```
o plane
v 0 0 2
v 0 2 0
v 2 0 0
f 1 2 3
# note missing o <name>
v 1 1 0
v 1 0 0
v 0 1 0
v 0 0 0
g curve
cstype bspline
curv 0 1 -1 -2 -3 -4
...
```

Fix wrong curve indices: missing parentheses.

Fix build issues after merge: BKE_* -> NOD_*

Also remove some extra paths from CMakeLists.txt.

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

Use MutableSpan instead of raw pointers

Since nearly all but one use cases for `copy_string_to_int`
is for single integer, MutableSpan only adds extra
`{&integer ,1}` syntax at the caller. Better use `int &r_dst`.

Also make exception `const`

Add assert before casting `int` to `uint` for MEdge.

Support meshes with edges with or without polygons.

Cleanup: Rename variables, use {} initialisation.

`{}` syntax would help catch when the C++ containers size() function
changes to `int64_t` since initialiser lists don't allow narrowing variables.

Specify that the strings are `_split`.

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

Move stoi into a function; Add exception handling

Also add comments for utility functions.

Also make `string` a `const &`; prefix return variables with `r_`.

Use `string::empty()` instead of comparing it with "" (clang-tidy).

Rename: mesh_from_bm_ to mesh_from_ob_