v3-rc1: Heatmap and surface plot of f(x,y) via texture Computes the plot of a function $z=f(x,y)$ of two parameters, generating float pixmap, which is then used as a texture to pass those values to the shader, which then draws the result. This is done both for heatmap (line in 'v2-heatmap-rescaledValue'), and for the surface plot, the latter of which is shown as the cloud of points (drawn using glDrawArrays()). The compute kernel (be it on CPU or GPU) rescales $z$ values to be in the [0.0, 1.0] range (assuming given range; some of values fall outside it, to show how colormap handles such values). The function to draw is hardcoded in plot2d_common.hpp as `func(x,y)`, and cannot be changed at runtime. The min-max rescaling is implemented by `rescaledValue()`. The colormap code is embedded in the fragment shader, as `colormap()` function in the 'glsl/texture.frag' and in the 'glsl/plot2d.vert' shaders (duplicated code). Simple grayscale colormap (`vec4(x, x, x, 1.0)`) is used, with overflow marking (blue, or vec4(0,0,1,1), for values smaller than expected minimum value, and red, or vec4(1,0,0,1) for values above expected maximum).