Consolidate Vec/Coord into the geom submodule

Also add the missing coord.rs to version control...
It should have been checked in earlier

src/render.rs

@@ -1,9 +1,8 @@
 use ansi_term::Color::RGB;
-use crate::geom::Vec2;
+use crate::geom::{Vec2, Vec3};
 use crate::{flt::{Flt, Real}, Material as _};
 use crate::mat;
 use crate::sim::{Cell, GenericSim};
-use crate::vec::Vec3;
 use crate::meas::AbstractMeasurement;
 use font8x8::{BASIC_FONTS, GREEK_FONTS, UnicodeFonts as _};
 use log::trace;