unify new/free() functions 2

unify new/free() functions 2

'Free' functions:
- Name ends in `_free()`
- Take a `**ptr`
- Creates a native pointer
- Sets pointer to `NULL`

Functions changed:
- color_line_free()
- mutt_actx_free()
- mutt_attachmatch_free()
- mutt_autocrypthdr_free()
- mutt_autocrypt_db_account_free()
- mutt_autocrypt_db_gossip_history_free()
- mutt_autocrypt_db_peer_free()
- mutt_autocrypt_db_peer_history_free()

'New' functions:
- Name ends in `_new()`
- Must be a 'new' function if there's a 'free' function

Functions changed:
- class_color_new()
- color_line_new()
- hash_new()
- mutt_actx_new()
- mutt_attachmatch_new()
- mutt_autocrypthdr_new()
- parameter_new()
- pgp_keyinfo_new()