Ship the three C4 examples and model:scaffold --example

- examples/: c4-standard-web-app, c4-e-shop (was online-shop),
  c4-event-based-integration; the same models the extension offers
  under Archify | New Model…
- model-scaffold --example <name> copies one and renames id, name,
  description and the overview title; never overwrites
- tests cover every example and the copy; docs updated

examples/c4-e-shop/main.archify

@@ -0,0 +1,24 @@
+schema_version: 1
+model:
+  id: e-shop
+  name: E-Shop
+  description: >
+    The web shop, its API and workers, and the stores behind them.
+    Context, containers and components, C4 style.
+diagram_type: architecture
+meta:
+  title: E-Shop — overview
+  output: main.html
+components:
+  - ref: customer
+    pos: [40, 160]
+    size: [130, 60]
+  - ref: shop
+    pos: [250, 160]
+    size: [150, 60]
+  - ref: psp
+    pos: [480, 160]
+    size: [150, 60]
+connections:
+  - { from: customer, to: shop, label: buys, variant: emphasis }
+  - { from: shop, to: psp, label: charges }