Fix: Cannot serve off /.../index.html

Docsify must be hosted on a server that supports a default directory
index (i.e. maps `/.../` -> `/.../index.html`).

Some platforms do not support this, however. For example, HTML apps
hosted on the popular game/software platform, Itch.io.

This change supports hosting Docsify off an explicit path file, such as
`/index.html`. It does this by:

 1. Adding handling for paths like `index.html#/blah`, and
 2. Normalising paths with fragments back to markdown paths

For example, `http://example.org/index.html#/blah` would be mapped to
`http://example.org/blah.md`.

This fixes:

#427

src/core/router/history/hash.js

@@ -18,7 +18,10 @@ export class HashHistory extends History {
     const path = window.location.pathname || '';
     const base = this.config.basePath;
 
-    return /^(\/|https?:)/g.test(base) ? base : cleanPath(path + '/' + base);
+    const basePath = path.endsWith('.html')
+      ? path + '#/' + base
+      : path + '/' + base;
+    return /^(\/|https?:)/g.test(base) ? base : cleanPath(basePath);
   }
 
   getCurrentPath() {

src/core/router/util.js

@@ -76,8 +76,15 @@ export const resolvePath = cached(path => {
   return '/' + resolved.join('/');
 });
 
+function normaliseFragment(path) {
+  return path
+    .split('/')
+    .filter(p => !p.includes('#'))
+    .join('/');
+}
+
 export function getPath(...args) {
-  return cleanPath(args.join('/'));
+  return cleanPath(args.map(normaliseFragment).join('/'));
 }
 
 export const replaceSlug = cached(path => {