Use chroma theme: dracula

Rather than defining all of the colours ourselves, we can simply choose
a theme that is supported by `chroma`.

examples/slides.md

@@ -1,6 +1,16 @@
 # Welcome to Slides
 A terminal based presentation tool
 
+```go
+package main
+
+import "fmt"
+
+func main() {
+  fmt.Println("Written in Go!")
+}
+```
+
 ---
 
 ## Everything is markdown
@@ -15,7 +25,6 @@ In fact this entire presentation is a markdown file
 ##### h5
 ###### h6
 
-
 # Markdown components
 You can use everything in markdown!
 * Like bulleted list
@@ -33,9 +42,11 @@ All you need to do is separate slides with triple dashes `---` on a separate lin
 like so:
 
 ```markdown
-Slide 1
+# Slide 1
+Some stuff
 
 --- 
 
-Slide 2
+# Slide 2
+Some other stuff
 ```