Use GET and support custom slugs

[MasterOfTheTiger]

This changes the URL shortener to use GET (and rudimentary support for POST) to process user input.

This also resolves #9 by adding support for custom slugs through the new slug GET parameter.

Known issues:

• There is not a workaround for URLs containing & in their URL (I will finish this in future commits to this pull request)
• If using POST and password protection, note that the password is passed along via GET when clicking the link to view a specific slug's stats

I am sure I took too much liberty and changing some things, so many things probably need to be changed before this is merged.

[MasterOfTheTiger]

Sorry about not working on this. My computer broke and I was unable to do PHP development. I will get back onto it now.

[tylerhall]

👍

[MasterOfTheTiger]

I need to get a development environment set up. I don't know how to do mod_rewrite for PHP development, and I can't find the router script I used for it before.

[tylerhall]

https://clickontyler.com/virtualhostx/

[aaronkollasch]

$custom_slug should be escaped before it's used in mysql_query on lines 84 and 97.

Suggested change

	$custom_slug = isset($_POST['slug']) ? '' : $_GET['slug'];
	$custom_slug = mysqli_real_escape_string($db, isset($_POST['slug']) ? '' : $_GET['slug']);