Improve alignment of text nodes in make-cd

[jonsterling]

Currently text nodes in a commutative diagram are vertically aligned on their baseline. This is an intuitive and reasonable default, but unfortunately it results in incorrect behavior when combined with snapping; in particular, there are many cases (depending on the physical height of a piece of math text) where drawing a fully horizontal or fully vertical arrow from one math node to another is impossible to achieve with precision, and instead it snaps to something that is at a strange angle. This problem is solved by setting the vertical alignment to be centered.

I am not sure that this is the actual best solution, but it solved the immediate problem for me. What do you think?

P.S. I have not yet succeeded in building TeXmacs on my machine, so I have just edited this code blindly --- so please don't merge unless you try it out. The way I tested this functionality was to create a new function in my own TeXmacs initialization script and add my own custom menu item for the new function.

[mgubi]

Note that you do not need to build TeXmacs in order to modify the scheme code. You can either overwrite the scheme files in your local TeXmacs $TEXMACS_PATH (on the Mac they are somewhere like /Applications/TeXmacs.app/Contents/Resources/share/TeXmacs/progs) or create a similar path in your $TEXMACS_HOME_PATH which usually is ~/.TeXmacs/progs. TeXmacs always look into $TEXMACS_HOME_PATH before resolving paths in $TEXMACS_PATH.

[jonsterling]

That's great to know, thank you!