Added callbacks for node errors and fifo overflow

Add new doc system which should/might deploy to pages.

mkdocs.yml

@@ -0,0 +1,50 @@
+site_name: KPN++
+site_description: A C++20 Kahn Process Network library
+repo_url: https://github.com/yourusername/kpn
+repo_name: kpn
+
+theme:
+  name: material
+  palette:
+    - scheme: slate
+      primary: indigo
+      accent: indigo
+  features:
+    - navigation.tabs
+    - navigation.sections
+    - navigation.top
+    - content.code.copy
+    - content.code.annotate
+
+nav:
+  - Home: index.md
+  - Getting Started: getting-started.md
+  - Concepts:
+    - Nodes: nodes.md
+    - Networks: network.md
+    - Channels: channels.md
+  - Error Handling & Events: error-handling.md
+  - Advanced:
+    - Static Networks: static-network.md
+    - Shared Resources: shared-resource.md
+    - Fan-out & Routing: fanout.md
+  - Examples: examples.md
+
+markdown_extensions:
+  - admonition
+  - toc:
+      permalink: true
+  - pymdownx.highlight:
+      anchor_linenums: true
+      line_spans: __span
+      pygments_lang_class: true
+  - pymdownx.inlinehilite
+  - pymdownx.superfences
+  - pymdownx.tabbed:
+      alternate_style: true
+  - pymdownx.snippets:
+      base_path: ['.']
+      check_paths: true
+  - pymdownx.details
+  - attr_list
+  - md_in_html