fix: correct handedness of polygon application in some cases (#50)

Resolves #49.
Also adds a special-case hack to correct a small error in Joyce's rendition of Book II, Prop 14. (That the error is truly in Joyce's spec rather than adapptlet is shown by the screenshot, which has an incorrect diagram.)

With this PR, as far as I know all diagrams in Books I and II work,

Reviewed-on: #50
Co-authored-by: Glen Whitney <glen@studioinfinity.org>
Co-committed-by: Glen Whitney <glen@studioinfinity.org>

src/adapptlet.civet

@@ -583,7 +583,11 @@ classHandler: Record<JoyceClass, ClassHandler> :=
             commands.push `${name} = Translate(${source}, ${displacement})`
          'first'
             unless args.subpoints then return
-            commands.push `${name} = ${args.subpoints[0]}`
+            // HACK: Special-case correction for Joyce Elements Bk II, prop 14
+            index .= 0
+            if name === 'H' and args.line and args.line[0] === 'HH2'
+               index = 1
+            commands.push `${name} = ${args.subpoints[index]}`
          /fixed|free/
             unless args.scalar then return
             coords := vertFlipped(args.scalar, cdata)
@@ -875,10 +879,10 @@ classHandler: Record<JoyceClass, ClassHandler> :=
             else if method is 'application'
                unless pt.length is 3 then return
                unless args.polygon?.length is 1 then return
-               direction := `UnitVector(${pt[0]} - ${pt[2]})`
+               direction := `UnitVector(${pt[2]} - ${pt[0]})`
                angle := `Angle(${pt[1]},${pt[0]},${pt[2]})`
                length := `Area(${args.polygon})`
-                  + `/(Distance(${pt[0]},${pt[1]})*sin(${angle}))`
+                  + `/(Distance(${pt[0]},${pt[1]})*abs(sin(${angle})))`
                commands.push ...[0..1].map (n) =>
                   `${aux}${n} = ${pt[n]} + ${length}*${direction}`
                auxiliaries.push aux+0, aux+1