New "browse" UI

Also, separated out browse, ?meta, and ?module request handlers.

Fixes #82

modules/utils/getLanguageName.js

@@ -0,0 +1,36 @@
+import getContentType from './getContentType.js';
+
+const contentTypeNames = {
+  'application/javascript': 'JavaScript',
+  'application/json': 'JSON',
+  'application/octet-stream': 'Binary',
+  'application/vnd.ms-fontobject': 'Embedded OpenType',
+  'application/xml': 'XML',
+  'image/svg+xml': 'SVG',
+  'font/ttf': 'TrueType Font',
+  'font/woff': 'WOFF',
+  'font/woff2': 'WOFF2',
+  'text/css': 'CSS',
+  'text/html': 'HTML',
+  'text/jsx': 'JSX',
+  'text/markdown': 'Markdown',
+  'text/plain': 'Plain Text',
+  'text/x-scss': 'SCSS',
+  'text/yaml': 'YAML'
+};
+
+/**
+ * Gets a human-friendly name for whatever is in the given file.
+ */
+export default function getLanguageName(file) {
+  // Content-Type is text/plain, but we can be more descriptive.
+  if (/\.flow$/.test(file)) return 'Flow';
+  if (/\.(d\.ts|tsx)$/.test(file)) return 'TypeScript';
+
+  // Content-Type is application/json, but we can be more descriptive.
+  if (/\.map$/.test(file)) return 'Source Map (JSON)';
+
+  const contentType = getContentType(file);
+
+  return contentTypeNames[contentType] || contentType;
+}