implement live-reloading dev server

Squashed commit of the following:

commit 02f077432202af4d633eb2cad81dfdaa6921317f
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Sat Apr 27 21:09:14 2024 +0200

    builder: only remove output directory if set and in dev mode

commit 47001e01c55fa6e74aafeda04ebc3e4e7c47eba0
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Sat Apr 27 21:03:37 2024 +0200

    implement live reload on dev server

commit 411ec969f61e4b73439f1c54ea29f75135ecc618
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Sat Apr 27 20:59:26 2024 +0200

    server: implement graceful shutdown

commit 5400132eb6eb1b638e0b3fd4265f51611c92d473
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Sat Apr 27 20:41:07 2024 +0200

    add some debug logs

commit 3c9b678197c044603950232d222f501ef74d7873
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Sat Apr 27 20:39:09 2024 +0200

    prefix log output with executable name

commit 300e24c179e390e9d3f5aeab4471c97f17f1fa64
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Sat Apr 27 20:29:42 2024 +0200

    don't panic inside internal packages, return error instead

commit fe2715d330402ad67fe866471bed89c7238ad2ec
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Fri Apr 26 01:18:29 2024 +0200

    config: use a table to configure CSP headers

commit d012553aaf78a436fa8871830b5d720a9e292d4b
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Thu Apr 25 17:13:39 2024 +0200

    dev: create basic dev server to build and serve from a temporary directory

commit a1d11d3e69650d9b43ca1b1d7b7ccc05a808d5c1
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Thu Apr 25 13:02:22 2024 +0200

    remove unused redirect_other_hostnames config option

commit fd67b19b5c7f76f0c3579e8a05ef20a618e90be7
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Thu Apr 25 12:58:53 2024 +0200

    server: make port a string, which is what go uses

commit c798e8e736c0649008cade337158399470a9099b
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Thu Apr 25 12:58:33 2024 +0200

    config: remove unused port variable

commit f94882b9001f3b0855e26b26b4a84b96e3deb22b
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Thu Apr 25 12:49:10 2024 +0200

    re-organise module layout

1 files changed, 0 insertions, 121 deletions

diff --git a/cmd/build/posts.go b/cmd/build/posts.go
deleted file mode 100644
index f03caf3..0000000
--- a/cmd/build/posts.go
+++ /dev/null
@@ -1,121 +0,0 @@
-package main
-
-import (
-	"bytes"
-	"log/slog"
-	"os"
-	"path"
-	"path/filepath"
-	"slices"
-	"strings"
-	"time"
-
-	"github.com/adrg/frontmatter"
-	mapset "github.com/deckarep/golang-set/v2"
-	"github.com/pkg/errors"
-	"github.com/yuin/goldmark"
-	"github.com/yuin/goldmark/extension"
-	htmlrenderer "github.com/yuin/goldmark/renderer/html"
-)
-
-type PostMatter struct {
-	Date        time.Time `toml:"date"`
-	Description string    `toml:"description"`
-	Title       string    `toml:"title"`
-	Taxonomies  struct {
-		Tags []string `toml:"tags"`
-	} `toml:"taxonomies"`
-}
-
-type Post struct {
-	Input    string
-	Output   string
-	Basename string
-	URL      string
-	Content  string
-	PostMatter
-}
-
-type Tags mapset.Set[string]
-
-var markdown = goldmark.New(
-	goldmark.WithRendererOptions(
-		htmlrenderer.WithUnsafe(),
-	),
-	goldmark.WithExtensions(
-		extension.GFM,
-		extension.Footnote,
-		extension.Typographer,
-	),
-)
-
-func getPost(filename string) (*PostMatter, []byte, error) {
-	matter := PostMatter{}
-	content, err := os.Open(filename)
-	defer content.Close()
-	if err != nil {
-		return nil, nil, errors.WithMessagef(err, "could not open post %s", filename)
-	}
-	rest, err := frontmatter.MustParse(content, &matter)
-	if err != nil {
-		return nil, nil, errors.WithMessagef(err, "could not parse front matter of post %s", filename)
-	}
-
-	return &matter, rest, nil
-}
-
-func renderMarkdown(content []byte) (string, error) {
-	var buf bytes.Buffer
-	if err := markdown.Convert(content, &buf); err != nil {
-		return "", errors.WithMessage(err, "could not convert markdown content")
-	}
-	return buf.String(), nil
-}
-
-func readPosts(root string, inputDir string, outputDir string) ([]Post, Tags, error) {
-	tags := mapset.NewSet[string]()
-	posts := []Post{}
-	subdir := filepath.Join(root, inputDir)
-	files, err := os.ReadDir(subdir)
-	if err != nil {
-		return nil, nil, errors.WithMessagef(err, "could not read post directory %s", subdir)
-	}
-	outputReplacer := strings.NewReplacer(root, outputDir, ".md", "/index.html")
-	urlReplacer := strings.NewReplacer(root, "", ".md", "/")
-	for _, f := range files {
-		pathFromRoot := filepath.Join(subdir, f.Name())
-		if !f.IsDir() && path.Ext(pathFromRoot) == ".md" {
-			output := outputReplacer.Replace(pathFromRoot)
-			url := urlReplacer.Replace(pathFromRoot)
-			slog.Debug("reading post", "post", pathFromRoot)
-			matter, content, err := getPost(pathFromRoot)
-			if err != nil {
-				return nil, nil, err
-			}
-
-			for _, tag := range matter.Taxonomies.Tags {
-				tags.Add(strings.ToLower(tag))
-			}
-
-			slog.Debug("rendering markdown in post", "post", pathFromRoot)
-			html, err := renderMarkdown(content)
-			if err != nil {
-				return nil, nil, err
-			}
-			post := Post{
-				Input:      pathFromRoot,
-				Output:     output,
-				Basename:   filepath.Base(url),
-				URL:        url,
-				PostMatter: *matter,
-				Content:    html,
-			}
-
-			posts = append(posts, post)
-		}
-	}
-	slices.SortFunc(posts, func(a, b Post) int {
-		return b.Date.Compare(a.Date)
-	})
-	return posts, tags, nil
-}