Implement changes review Els

[wlangera]

Changes after review and meeting with @ElsLommelen (#7)

• update new function name autoqmd_insert_children() in vignette
• improve and/or add error and warning messages for users
• add argument child_labels to autoqmd_prepare()
• placeholder message above include part and only add once (maybe check if there is no comment above), remove feature from post render

Create metadata in child files:

• move template deps to generate children function
• add freeze to metadata true or false, use this for warning generation by finalise combination freeze and delete
• add dependency stamp to metadata in child files in case of YAML children insert? If this works, also do for QMD insert and create helper to extract it and add it to QMD file

[wlangera]

No extra work needs to be done for dependency stamp, you can now use freeze for both quarto books and websites. I explained it a bit better now in the vignette.