Having two consecutive image inclusion lines causes NotImplementedError

[TymekDev]

Describe the bug
Having two consecutive image inclusion lines (without a blank line in between) causes NotImplementedError to be raised.

To Reproduce
Add two image source lines. Example of slides below.

Expected behavior
An error informing that the image source lines should be separated by a blank line.

Slides

# Good

![img](image.png)

![codio](codio.yaml)

---

# Bad

![img](image.png)
![codio](codio.yaml)

Environment

• OS: Ubuntu 20.04.1 LTS
• Terminal emulator: kitty
• Python version: 3.8.2
• present version: 0.5.1

Additional context
This is similar to #82 but I filed this separately because I would expect different errors from both. I also suspect that the root cause is different for both of these.

[vinayak-mehta]

Thanks for reporting this!