Add work-in-progress 2.0 guides.

These are a combination of existing 1.3 materials and new work, including by @swilgosz

Relevant source PRs:

#99
#101
hanami/guides-v2#1

content/v2.0/_index.md

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+---
+version: v2.0
+---

content/v2.0/actions/_index.md

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+---
+title: Actions
+order: 50
+---

content/v2.0/actions/overview.md

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+---
+title: Overview
+order: 10
+aliases:
+  - "/actions/overview"
+---
+
+## Actions
+
+In a Hanami application, actions are responsible for handling HTTP requests. Actions decide what HTTP response your application returns for a given request - its status, body, headers, whether to issue a redirect, and so on.
+
+Every action in your Hanami application is an individual class. Actions define a `#handle` method which takes two arguments: `request`, an object representing the incoming request, and `response`, an object representing the outgoing response.
+
+Modifying the response object allows you to control how your application responds to a request.
+
+```ruby
+# app/actions/books/show.rb
+
+# frozen_string_literal: true
+
+module Bookshelf
+  module Actions
+    module Books
+      class Show < Bookshelf::Action
+        def handle(request, response)
+          id = request.params[:id]
+
+          response.body = "You requested book #{id}"
+        end
+      end
+    end
+  end
+end
+```
+
+Let's take a deeper look.
+
+## Parameters
+
+The parameters associated with an incoming request are available via the `#params` method on the `request` object.
+
+Available parameters are surfaced from variables specified in the router (`/books/:id`), query strings (`/books?page=2`), and request bodies (for example a `POST` request to `/books` from a form submission).
+
+```ruby
+def handle(request, response)
+  # GET /books/1
+  request.params[:id] # => "1"
+
+  # GET /books?category=history&page=2
+  request.params[:category] # => "history"
+  request.params[:page] # => "2"
+end
+```
+
+**Remainder of parameters under construction**
+
+
+## Under construction
+
+Topics to cover:
+
+- request and response
+- mime types and format
+- control flow
+- params (including req.ar.to_h) and query string parameters.
+- param validation
+- request headers
+- response headers
+- redirects
+- halt
+- exception handling
+- HTTP caching
+- inheritence
+- Testing
+
+Relevant PRs:
+
+[https://github.com/hanami/guides/pull/101](https://github.com/hanami/guides/pull/101)

content/v2.0/architecture/_index.md

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+---
+title: Architecture
+order: 60
+---