Adding surfaceEncoding

This MR contains surface encoding and decoding to/from SurfaceBackend. Questions & problems:

1. SurfaceBackend has bounds implemented as floats, while the bound values are doubles. This requires double<->float conversions. Wouldn't it be more elegant to store bound values as doubles? we store all values in SurfaceBackend as floats to save space
2. Curvilinear surface not implemented it seems we do not need this shape
3. It looks like geometry context is not needed by surface decoding (or I don't understand something). We maybe might remove it from function call. geometry context stays in the function call, but is not used.

Tagging @pagessin @cvarni @ncalace @tbold @emoyse @goetz @adye