Support MTL files with escaped whitespace

[chapulina]

As suggested on comment #46 (comment), this adds support for MTL files containing whitespaces, as long as the whitespaces are escaped with \ inside an OBJ file.

I wasn't sure if it was ok to change the signature of the SplitString function. I could hardcode the escape character inside the function if that's preferred.

Added a test that demonstrates a combination of files with and without spaces.

I tried to keep the code style from the rest of the files, but please let me know if anything needs to be udpated.

I also added a couple of dependencies that weren't listed on the viewer example and that I needed to make it work.

[syoyo]

@chapulina Awesome!

TinyObjLoader still want to support C++03, so C++11 for loop need to rewrite(And I need to setup CI build with C++03 mode)

Others looks nice. Let me give some time to test PR on my local environment.

[chapulina]

TinyObjLoader still want to support C++03, so C++11 for loop need to rewrite

Oops, muscle memory. Updated in 350d32a.

Let me give some time to test PR on my local environment.

Thanks!

[syoyo]

Updated in 350d32a.

Thanks! My local tests works well so merged!

Also, I made C++03 mode default in Travis CI.

[chapulina]

Thanks, @syoyo ! What's the process to get a new version tagged? Would it be possible to get a v1.8 anytime soon?

[syoyo]

@chapulina I have already tagged new version as v2.0.0rc8(we are moving to v2.0.0): https://github.com/tinyobjloader/tinyobjloader/releases/tag/v2.0.0rc8