use a common lua string for tests
Add lkonf_getkey_boolean()

* Provide lkonf_getkey_boolean(); get boolean value at iKeys.
  Similar to lkonf_get_boolean(), except that keys invalid in '.'-separated
  path may be used.
* Provide lkonf_keys typedef for array of keys.
* Internal lki_find_table_by_keys(); lkonf_keys equiv to lki_find_table().
Rename lkonf_t to lkonf_context.

Rename lkonf_t to lkonf_context.
Rename argument 'iLk' to 'iLc'.
Document lkonf_getkey_boolean()
rename lkonf_s -> lkonf_context_s
improve doxygen for internal APIs
expand lkonf_getkey_boolean() tests
test getkey_boolean
use last (not first) key in getkey error message

* Add "size_t * oMatch" to lki_find_table_by_keys(). If not NULL, set to
  index of last key if LK_OK.
* Adjust lkonf_getkey_boolean() to use last key in type mismatch errors.
regen
rename find_table* sources to match method names