Reading code block with empty line returns incorrect format

[Takashi Kato]

This should print pre but code

(import (rnrs) (text markdown) (pp))

(pp (string->markdown
          "```
foo

bar
```"))

[Takashi Kato]

Formatting code block

[Takashi Kato]

Handling empty line in ``` stile verbatim. (Fixes #136)

→ <<cset 8052ea7108a5>>