Release Notes for v0.3.0

This version introduces breaking changes. Please see example.c in the source
root directory for usage.

Notable changes:

  * Use dynamic memory allocation for keys, values, and attributes.
  * canfigger_free() replaced with canfigger_free_current_key_node_advance()
  * canfigger_free_attr() removed
  * use 'canfigger_free_current_attr_str_advance()' instead of
    'list->attr_node = list->attr_node->next'
  * In meson.build, rename dep_canfigger->canfigger_dep
  * lines starting with '[' are ignored
