Markdown

I made a bunch of changes, none of which will affect visitors to the site.

1.  Used Jekyll's markdown magic to render markdown resources like Zack's intro-git talk
2.  Moved all blog posts that were originally categorized as "resource" to be categorized as "link" and changed their yaml front matter from `link: someurl` to either `slides: someurl`, `code: someurl`, or both
3.  Added a folder in `/learn/_posts/` where markdown resources will live and be rendered from
     - Note that because I am rendering resources as blog posts, they should have the url `adicu.com/YYY-MM-DD/name-of-post.html` but with automated, programatic redirecting, they are now `adicu.com/name-of-post/`
4.  Totally revamped `newpost.sh` so that it
     - runs with the form `./newpost.sh blogpost|resource|link <name>` where `<name>` is all lowercase with words separated by dashes
     - actually checks for valid input
     - if the type is `resource`, put the new file in `/learn/_posts/` and inject its permalink into the yaml front matter accordingly
5.  Move `intro-webdev`, `intro-python` and `intro-git` to use this new rendering method
6.  Redirect `/intro-webdev/` -> `/learn/intro-webdev` and `/intro-webdev/python/` -> `/learn/intro-python/`

In order for people to use the new system to add a new markdown resource they do the following:

```bash
$ ./newpost.sh resource intro-awesome
Created new resource in learn/_posts/YYYY-MM-DD-intro-awesome.md
$ vim learn/_posts/YYYY-MM-DD-intro-awesome.md
# change the title front matter, and copy/paste their markdown
```

Blog writers use a slightly modified, but definitely improved:

```bash
$ ./newpost.sh blogpost my-blog-post
Created new blogpost in _posts/YYYY-MM-DD-my-blog-post.md
$ vim _posts/YYYY-MM-DD-my-blog-post.md
# change the title front matter, and copy/paste their markdown
```