bug: Transformed url does not respect custom slug

[techfg]

When a page contains a custom slug, the transformed url is not respecting it and instead, generating the astro default slug via githug-slugger.

For example, in a file /posts/post-3.md:

---
title: Post 3
slug: post.3
---

[Post 3](./post-3.md)

Should result in /posts/post.3 but instead results in /posts/post3.

It appears in #9 logic was added to handle special characters, etc. which makes sense and was needed. However, if a custom slug exists, it should use it.

Astro appears to handle this by generating the default slug but then checking for a custom slug and if exists, using it, else falling back on default.

Repro:

• https://stackblitz.com/edit/withastro-astro-7ge5gz

With Proposed Fixes from PR #21:

• https://stackblitz.com/edit/withastro-astro-mtqt5k

Steps to repro:

1. Open repro
2. Click on Post 1 link
3. Click on either link under Repro for Issue #14

Expected Result: Link should navigate to /posts/post.3 or /posts/archive.md/archive-1 (depending on link chosen)

Actual Result: The . is stripped and results in 404

Additional Info: You can see all links that Astro generates on home page under Issue #14 heading

[techfg]

FYI - Edited OP to a Stackblitz to the repro that contains the proposed fixes from #21.

[vernak2539]

Released in v0.9.0! Thanks!