mix.exs updates for consistency and more data

Mostly see #57 by @kianmeng

Decided to point the changelog to github though, as unreleased
changes are visible there which may come in helpful.

mix.exs

@@ -1,18 +1,19 @@
 defmodule BencheeHTML.Mixfile do
   use Mix.Project
 
+  @source_url "https://github.com/PragTob/benchee_html"
   @version "1.0.0"
+
   def project do
     [
       app: :benchee_html,
       version: @version,
       elixir: "~> 1.6",
       build_embedded: Mix.env() == :prod,
       start_permanent: Mix.env() == :prod,
-      docs: [source_ref: @version],
       deps: deps(),
+      docs: docs(),
       package: package(),
-      test_coverage: [tool: ExCoveralls],
       preferred_cli_env: [
         coveralls: :test,
         "coveralls.detail": :test,
@@ -25,11 +26,7 @@ defmodule BencheeHTML.Mixfile do
         plt_file: {:no_warn, "tools/plts/benchee.plt"}
       ],
       name: "benchee_html",
-      source_url: "https://github.com/PragTob/benchee_html",
-      description: """
-      HTML formatter with pretty graphs for the (micro) benchmarking library benchee.
-      Also allows export as PNG image!
-      """
+      test_coverage: [tool: ExCoveralls]
     ]
   end
 
@@ -64,13 +61,33 @@ defmodule BencheeHTML.Mixfile do
 
   defp package do
     [
+      description: """
+      HTML formatter with pretty graphs for the (micro) benchmarking library benchee.
+      Also allows export as PNG image!
+      """,
       files: ["priv", "lib", "mix.exs", "README.md"],
       maintainers: ["Tobias Pfeiffer"],
       licenses: ["MIT"],
       links: %{
-        "github" => "https://github.com/PragTob/benchee_html",
-        "Blog posts" => "https://pragtob.wordpress.com/tag/benchee/"
+        "Blog posts" => "https://pragtob.wordpress.com/tag/benchee/",
+        "Changelog" => "https://github.com/bencheeorg/benchee_html/blob/main/CHANGELOG.md",
+        "GitHub" => @source_url
       }
     ]
   end
+
+  defp docs do
+    [
+      extras: [
+        "CHANGELOG.md",
+        "CODE_OF_CONDUCT.md": [title: "Code of Conduct"],
+        "LICENSE.md": [title: "License"],
+        "README.md": [title: "Overview"]
+      ],
+      main: "readme",
+      source_url: @source_url,
+      source_ref: @version,
+      formatters: ["html"]
+    ]
+  end
 end