Added support for GLSL 3 shaders (GLSL 3.30 and GLSL ES 3.00).

To use GLSL 3 in a shader, the first line of the shader has to be: #pragma language glsl3

glsl1 is the default language.

Added “glsl3” graphics feature as part of the table returned by love.graphics.getSupported().

Added love.graphics.validateShader(boolean gles, shadercode). It returns a boolean along with an error string if the shader code has errors for its target language and platform (gles or desktop).

Implemented support for Core Profile OpenGL 3.3 in love.graphics.

--HG--
branch : minor

src/modules/graphics/opengl/Graphics.h

@@ -129,9 +129,12 @@ public:
 
 	bool isSupported(Feature feature) const override;
 	double getSystemLimit(SystemLimit limittype) const override;
+	Renderer getRenderer() const override;
 	RendererInfo getRendererInfo() const override;
 	Stats getStats() const override;
 
+	Shader::Language getShaderLanguageTarget() const override;
+
 private:
 
 	struct CachedRenderbuffer
@@ -143,6 +146,8 @@ private:
 		GLuint renderbuffer;
 	};
 
+	love::graphics::StreamBuffer *newStreamBuffer(BufferType type, size_t size) override;
+
 	void endPass();
 	void bindCachedFBO(const std::vector<love::graphics::Canvas *> &canvases);
 	void discard(OpenGL::FramebufferTarget target, const std::vector<bool> &colorbuffers, bool depthstencil);