Boostnote: TOC generator handles the heading "X" as a checkbox

[naoh40]

Current behavior

Trivial bug: a heading X results in a [X] in the TOC section, which will be rendered as a checkbox.

Expected behavior

I suggest this edge case be handled specially. For example, [ X] gives the wanted output.

Steps to reproduce

Simply generate the TOC for # X:

<!-- toc -->

- [X](#X)

<!-- tocstop -->
# X

Environment

• Version : 0.11.17

[arcturus140]

I found another edge case: # []

# X
# [ctrl]
# [link](google.com)
# - a
# * a
# + a

Environment

• Version: 0.11.12