Refactored YANG min/max validation code, created new clixon_validate_minmax.[ch]

Added new recursive minmax check for non-presence containers
This makes validation checks stricter, including check of incoming RPCs
Renamed xml_yang_check_list_unique_minmax() to xml_yang_minmax_recurse()
Fixed again: [YANG min-elements within non-presence container does not work](https://github.com/clicon/clixon/issues/355)

test/lib.sh

@@ -989,6 +989,7 @@ EOF
 # clixon tester read from file for large tests
 # Arguments:
 # - Command
+# - Expected retval
 # - Filename to pipe to stdin 
 # - expected stdout outcome
 function expecteof_file(){