Initial commit.

Just reads the YAML file, nothing else.
Removed "using namespace std" from main.c
Added "grid" as vector of grid voxels.
Added #ifndef to grid.hh
Added return value to int main().
Changed grid vector type from "GridVoxel" to "struct GridVoxel".

Since I didn't typedef the GridVoxel struct, I shouldn't be able to write just
"GridVoxel". Dunno why compiler didn't complain...
CMake: added C++11 compiler flags.

Because C++11 is #*$&ing amazing and everybody should use it.
main: removed fstream and exception headers.

We don't use them (yet), so stop including them.
Added ray class with initialization.

I'm trying to be really careful about avoiding explicit array indices, and
instead using iterators. It's challenging to do since indices seem so
fundamental to numerical methods, but some careful thought shows that most
indices don't actually mean anything at all; we usually apply the same
algorithm to grid functions of all indices. The only indices that really matter
are things like the following:

  - the one before the one I'm on now (use std::next)
  - the one after the one I'm on now (use std::prev)
  - the first one (use <container>::begin())
  - the last one (use <container>::end())
Added header file with a few physical constants.
Added Planck function.

Unused right now, just compiles. I chose the wavelength version instead of the
frequency version.
Added .bzrignore file.
Added wavelength as a class member of class Ray.
Added Ray class member function set_to_LTE().

Sets the source function along every point of a ray to the Planck function.
Removed debugging cout statement.
Changed member pointer of struct RayData to const pointer.

For now we just need the pointer to gather data from the grid; we don't want to
change the grid data (yet).
Added member function bind_to_grid() to Ray class.
Added overloaded "ostream<<" operator to Ray class for pretty printing.
Added call to bind_to_grid() in main().
Added temperature to GridVoxel struct.