Add rewritten config, dubbed emacs-siren

I've taken a lot of inspiration from Emacs-Prelude when it came to the
structure of this rewritten config. I didn't want to use Prelude as I
don't agree with all it's defaults, nor do I want to have to deal with
any future changes in Prelude that might break things for me. So instead
I went down the fully custom path, but heavily inspired by Prelude, both
in terms of file/code structure, and also some of it's features.

Compared to my old config setup, it's got most of the same things, but
nearly everything is in a module file now, making it easy to fully
enable/disable certain features.

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "vendor/tomorrow-night-paradise-theme"]
+	path = vendor/tomorrow-night-paradise-theme
+	url = https://github.com/jimeh/tomorrow-night-paradise-theme.el.git