Mesh generation -related wiki page

[SeSodesa]

I've added the beginnings of a wiki page specifically dedicated to mesh generation (link). It needs contributions from people who are knowledgeable on the topic, and specifically the internals of how Zeffiro builds the mesh.

This is because in order for users to be able to generate meshes programmatically, they would need to know all of the meshing-related fields of the project struct zef. Otherwise fine-tuning of the mesh will be impossible, if one does not wish to utilize the GUI.

I am not knowledgeable enough to be able to fill in all of the blanks without spending a long time studying the source code.