Starting on shader support.

- Added shader_program
- Updated coding_conventions
Working on shader support.

- Adding classes that will be used to define shaders.
Working on shader support. Just finished shader compilation, need to add compile error checking.

- Added resource_exception for use when a resource fails to load.
- Added file_string, for loading a text file into an in-memory string.
- Added message_exception and made fatal_construction_exception and resource_exception
  derive from it.
Separated shader into its own class even though it won't be used outside of shader_program. Correcting compile errors.
shader compiles, need to test.

- Renamed assert.h to error.h, added error.cpp.
- Modified error with overloads for char const* and unsigned char const*. The reason for the
  latter is that some OpenGL APIs (GLEW namely in my case) return strings of unsigned chars
  for some error reporting mechanisms (glewGetErrorString).
- Verified LE_ERROR message box works.