include: cyclic references cause stack overflow

[sijie123]

Tell us about your environment

• NodeJS v9.3.0
• MarkBind Version: v1.16.1

What did you do? Please include the actual source code causing the issue.

a.md

<include src="b.md" />

b.md

<include src="a.md" />

What did you expect to happen?
The includes should be resolved automatically. At least, a user-friendly error should given, to allow the user to understand what happens.

What actually happened? Please include the actual, raw output.
MarkBind errored with a RangeError.

error: RangeError: Maximum call stack size exceeded
Error while preprocessing '/path/to/file/a.md'

However, the RangeError and "Maximum call stack size" error isn't helpful in determining what went wrong.