Textures can have mipmaps (And information for using textures)

I use a `Texture` `struct` that contains a `mipmap: bool`,
on creation:
```rust
if mipmap {
  C3D_TexInitMipmap(...)
} else {
  C3D_TexInit(...)
}
```
on texture upload:
```rust
C3D_TexUpload(...);
if mipmap {
  C3D_TexGenerateMipmap(...);
}
C3D_TexFlush(...);
```