Support for indention in markdown

[elfenpiff]

When having a markdown document with list one uses most likely geoffrey with indentation which is not supported at the moment.

Lorem ipsum.
1. blaa fuu
    <!--[geoffrey][iceoryx_examples/waitset/ice_waitset_basic.cpp][sig handler]-->
    ```cpp
    // indented code snippet, not supported

Bla fu

// non intended code snippet works

[elBoberido]

Just to be clear, you don't want to keep the indentation from the snippet but add the indentation from the markdown file if there is any?

[elfenpiff]

I would like to have two things:

1. At the moment geoffrey ignores the comment since it seems that there are no spaces and tabs allowed before the markdown comment.
2. geoffrey should insert the code with the same indentation as the geoffrey comment.