Type conversion article

[jonnew]

I asked this question on Discord and now it appeared again on the google groups: https://groups.google.com/g/bonsai-users/c/PVWceGOlo84/m/MaTsmz0TAQAJ. It might be nice to have an article explaining type conversion in general along with some common examples: mabye primative types via externalizing the Value, implicit conversion (e.g. Mat to IplImage), and explicit conversion via an ExpressionTransform.