Fix pkg-config file

libgends and lll have to go in Requires.private
Add lambda function macro
New slist API

- New data structure gds_inline_slist_node_t
- New data structure gds_slist_t, which uses this inline data structure
- Complete rewrite of slist API:
  - reworded:
    - add_first -> unshift
    - add_last -> push
    - del_first -> shift
    - del_last -> pop
  - deleted:
    - add_after
    - del_after
    - get_nth_node
    - get_last_node
    - add_list_first
    - add_list_after
    - add_list_last
  - added:
    - get
    - splice
    - slice
    - map
    - filter
    - reduce
- Add container_of macro
Move rbtree_inline.*,rbtree_fast_inline.* to inline/
Global comments reformatting: slist.h
Introduce new UNDEFINED macro
Remove 'low level' from slist.h description
Add missing copyright notices
Fix gds_inline_slist_node_append_list comment
New dlist API, similar to slist API