Fixed memory allocation, corrected parabola code
	The data is now a flat array, declared as a pointer and assigned as
	malloc( num_points*2*sizeof(GLfloat) )
	The call to glBufferData is given the correct size argument
	The v_parabola_by_a function has been changed:
	- void return type
	- GLfloat* output argument, to which the data is memcpy()-ed
	- The actual generation of data was adding an extra point,
	potentially causing memory corruption, this has been fixed