improved doc + moved examples to separate file

doc/example.typ

@@ -0,0 +1,41 @@
+#import "@preview/cetz:0.2.2": draw
+#import "../src/circuit.typ": circuit
+#import "../src/util.typ"
+
+#let example-preamble = "import \"../src/lib.typ\": *;"
+#let example-scope = (
+  draw: draw
+)
+
+#let example(src, show-src: true, vertical: false, fill: true) = {
+  src = src.text
+  let full-src = example-preamble + src
+  let body = eval(full-src, scope: example-scope)
+  let img = circuit(length: 2em, body)
+
+  block(width: 100%,
+    align(center,
+      box(
+        stroke: black + 1pt,
+        radius: .5em,
+        fill: if fill {util.colors.yellow.lighten(80%)} else {none},
+        if show-src {
+          let src-block = align(left, raw(src, lang: "typc"))
+          table(
+            columns: if vertical {1} else {2},
+            inset: 1em,
+            align: horizon + center,
+            stroke: none,
+            img,
+            if vertical {table.hline()} else {table.vline()}, src-block
+          )
+        } else {
+          table(
+            inset: 1em,
+            img
+          )
+        }
+      )
+    )
+  )
+}