Blender Git Loki

MTL: use mtllib for importing MTL files.

Create a utility function for splitting lines into the first words
& the rest of it.

MTL: release shader_output_ node instead of bsdf_.

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

Initial material creation support.

Cleanup: Use MutableSpan, add asserts

Remove passing of unnecessary variables.

Limit scope of `tex_image_filepath`.

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

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

Add MTL parser.

Add fallback value in string to number conversions

Remove remnant `stringstream s_line` which was used with `>>`
operator for storing floats and ints. That has been replaced
with `stof`/ `stoi`.

Limit the scope of MTL exporter's tex_node pointer.

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

Fix build error due to forward enum declaration

In full build, the following error happens. So fix it by including the
definition file before the forward declaration one.

```
In file included from source/blender/io/collada/SkinInfo.cpp:40:
source/blender/blenkernel/BKE_object_deform.h:62:6: error:
enumeration previously declared with nonfixed underlying type
enum eVGroupSelect
^
In file included from source/blender/io/collada/SkinInfo.cpp:36:
source/blender/makesdna/DNA_scene_types.h:2099:14: note:
previous declaration is here
typedef enum eVGroupSelect {
^
1 error generated.
```

Use VectorSet instead of vector for def_group.

The lookups are now faster and insertion order is also
retained since no item is removed from the `VectorSet`.

Also fix a leak that happened due to mishandling of the pointer
to the allocated memory of `MDeformWeight`.

Remove potentially confusing loop index that is used with
`tot_loop_idx`.

Cleanup: silence clang-tidy warnings; comments.

Use static_cast wherever applicable.

Pass struct by reference.

Remove unnecessary const qualifiers for primitive types.

Make some member functions static instead.

Remove intermediate non-owning pointers to new class instances.

Remove else in else-after-return.

Initialise variables at definition.

Keep vertex deform group names and def_nr in sync

I realised later on that Map is unordered, so the order of insertion,
on which def_nr depends, is not retained. So a Vector of strings
has been used & the index of the string-of-interest is the def_nr.

Unfortunately, it will be slow on large number of vertex groups.

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

Fix curve not being visible in Object mode.

Thanks to Howard Trickey(@howardt) for finding the fix!

Support importing vertex deform groups.

Remove unnecessary casting in exporter's deform group related code.

The fix in `BKE_object_deform.h` is temporary, until D8378
is committed to master.

Fix build errors due to wrong auto to type changes

They were the last changes I made and didn't build afterwards.

Cleanup: Fix typo in comments.

Move Object creation code in Mesh creation class.

This is required for setting deform groups which are a part of `Object` struct.

Also rename NurbsElem > OBJNurbsElem.

Remove forward declarations from *nurbs.hh & *mesh.hh files
since the cyclic dependency with *object.hh is removed.

Remove auto.