Add error checking for other serializable objects

[connorkuehl]

MoirePrimitive and PolygonPrimitive enforce their invariants when they're being serialized.

Like this:

impl<W: Write> PartialGerberCode<W> for PolygonPrimitive {
    fn serialize_partial(&self, writer: &mut W) -> GerberResult<()> {
        // Vertice count invariants
        if self.vertices < 3 {
            return Err(GerberError::MissingDataError("There must be at least 3 vertices in a polygon".into()));
        }
        if self.vertices > 12 {
            return Err(GerberError::RangeError("The maximum number of vertices in a polygon is 12".into()));
        }
        if self.diameter.is_negative() {
            return Err(GerberError::RangeError("The diameter must not be negative".into()));
        }

Other types (like VectorLinePrimitive, etc.) should do this too 😃