create a new function to combine getSVG and getMetrics

[omkelderman]

I had a need to get both the metrics and the SVG string at the same time. Now I could have just called getSVG and getMetrics in my code and be done with it, but I noticed that getSVG actually used getMetrics internally so then it would be called twice.

So I thought why not expose a function to get them both at the same time in an efficient manner.
This change is entirely backwards compatible.

[omkelderman]

hmm, I actually now just realized that the same can be done for getD and getPath, which also means that the current implementation of getSVG already calls getMetrics twice: once in getSVG itself and once in getD which gets called in getPath

This should be able to be optimised even more

[cmloegcmluin]

Great idea @omkelderman. I would certainly benefit from having this option.