Allow passing custom History object

[notpushkin]

This exposes a param on the router called history. By default, it will use globalHistory, but we can pass an API-compatible history object and it will be used instead. For example, we can force it to use a memory source (closes #153):

<script>
  import { Router, Link, Route } from "svelte-routing";
  import {
    createHistory,
    createMemorySource,
  } from "svelte-routing/src/history";
  // ...import routes...

  const source = createMemorySource();
  let url = source.location.pathname;
  const history = createHistory(source);
</script>

<Router url="{url}">
  <nav>
    <Link to="/">Home</Link>
    <Link to="about">About</Link>
    <Link to="blog">Blog</Link>
  </nav>
  <div>
    <Route path="blog/:id" component="{BlogPost}" />
    <Route path="blog" component="{Blog}" />
    <Route path="about" component="{About}" />
    <Route path="/"><Home /></Route>
  </div>
</Router>

I've also noticed that the History type is kinda like the history package used in React Router – apart from navigate vs. push/replace, it seems like a drop-in replacement. You might want to switch to that instead, as it seems like a good abstraction overall – but that's up to you :)

[notpushkin]

Note that this breaks the import { navigate } from "svelte-routing" function. I'm not yet sure how to replace it, since we have to call getContext during component initialization, but I think it can be dealt with somehow (pass history object to the route?).

[krishnaTORQUE]

Hi
I forked svelte-routing > https://github.com/krishnaTORQUE/svelte-routing-next.
And I merged your PR there.
Please let me know if you have any query.
Thanks.

[krishnaTORQUE]

MERGED
View Changelog: https://github.com/EmilTholin/svelte-routing/blob/master/CHANGELOG.md