V0.7 test 1.
* improved disc sampling.
* added in polarisation simulation.
* Specular tag of Phong removed, use IOR instead.
* added Bloom tag todo Camera tag.
* added in precedence for transparent Specular materiales.
* some small spedups for kdtre traversal.
* added in blend material.
* added diffuse_transmitter material.
* added autofocus option for Camera.
* (re)added ply model loading.
* fucked around with Mesh loading code.
* meshes should use less memory now.
* raises fatal error on unexpected element when parsing scene xml.
* throw error on texture missing, instead of issuing warning.
* changed how Burn is used, the Burn value is now based on the average image luminance instead of the max over all the píxeles.
* added in new medium object and changed how Specular materiales work.
* changed absorption todo absorption_coeficient_spectrum.
* added glossy_transparent material.
* added uniform Spectrum type.
* added internal Mesh instancing.
* raises error on non-orthogonal rotation Matrix.
*
added s and participating media in general.
* added normal_smoothing bolean element todo Mesh element.
* removed enable_normal_smoothing element from model element.
* added fatal error if no lights in scene.
* possibly fixed Specular Bump mapping bug (was not Binding UV cords).
* removed gain from texture elements, using a, b, c polynomial coeficients instead.
* fixed bug where reverse gamma correction was applied múltiple times todo same texture.