Change Input and Output based on RFC description

[Filip-Vitkovsky]

Input and Output statements have defined mandatory data-def-stmt in bnf, but in the description provided in RFC all statements inside input and output have 0..n cardinality, which creates a problem when validating yangs.

• RFC description :
  +--------------+---------+-------------+
  | substatement | section | cardinality |
  +--------------+---------+-------------+
  | description | 7.21.3 | 0..1 |
  | grouping | 7.12 | 0..n |
  | if-feature | 7.20.2 | 0..n |
  | input | 7.14.2 | 0..1 |
  | output | 7.14.3 | 0..1 |
  | reference | 7.21.4 | 0..1 |
  | status | 7.21.2 | 0..1 |
  | typedef | 7.3 | 0..n |
  +--------------+---------+-------------+

• RFC bnf:
  input-stmt = input-keyword optsep
  "{" stmtsep
  ;; these stmts can appear in any order
  *must-stmt
  *(typedef-stmt / grouping-stmt)
  1 *data-def-stmt
  "}" stmtsep

File with error: cisco-svo-hl-controller-group.txt

• Change bnf generation in RFCParser for input and output and change or delete checks for these statements in annotator.