HardwareBuffer class renamed to glHardwareBuffer
FileReader: Added own_file_content parameter to the class' constructor

This parameter is used to determine whether the class should delete the
fileContent_ pointer in the destructor or not.
Shader class renamed to glShader
Program class renamed to glProgram
Added newMaterial to BackendLocator + implemented in backend/opengl
glProgram uses a local function instead of a class method to check the shader link status
glShader uses a local function to check shader compilation status instead of a class method
initial implementations of opengl/Material
Added IMaterial interface
Removed IShader interface
Renamed BackendLocator into EngineBackend
added doc/ directory to .gitignore
changed include style from <IModel.h> to "IModel.h" in IRenderer.h
Added setNamedUniform method to the IMaterial interface
Added void clear() methods to the gl_* classes in opengl/
Added the opengl/Shader class used to compile and link a complete GPU program