141013-2216 Big improvements

This will be the last improvement to our "Simple Triangular" drawings.
Then we will be mainly focused on Texture Rendering.

Firstly, the readFromObjFile function is optimized, and now it takes
much less time to load a *.obj file.

Secondly, I created useful functions from some repeatedly called codes.

Thirdly, I created another function to read *.obj file, which can create
multiple models from one *.obj file. And this is very helpful if we want
to modularize our project.

I consider it a big improvement, because now, adding a different object
into scene only requires us to add two or three lines in the code.

By Zhongzhi Yu (Mark)