Add support for @inherit in summary to be replaced by the parent summary

[Stefan Glase]

As a user I want to use the parent summary in my subtasks. As an advanced user I want to be able to escape @inherit so that it is not replaced by the parent summary.

Examples

positive examples:

- Use the parent text here: @inherit
- Test @inherit
- Implement @inherit

negative examples:

- Do not use the parent text here: \@inherit

Regular Expression

This regular expression will only find and replace non-escaped keywords:

(?<!\\)@inherit

Tasks

• implement replacement for @inherit
• implement replacement for \@inherit to @inherit
• add documentation for syntax