fix(definitions): comments filtering

[beeb]

According to the rules implemented by solc, the only comments that constitute NatSpec are:

• The last multiline doc-comment before a definition
• The block of last contiguous single-line doc-comments before a definition

/// @dev This should be ignored
/**
  * @dev This should be ignored
  */
/// @notice  This is NatSpec
/// @param a This is NatSpec
function foo(uint256 a) internal { }

/// @dev This should be ignored

/// @notice  This is NatSpec
/// @param a This is NatSpec
function foo(uint256 a) internal { }

/**
 * @dev This should be ignored
 */
/**
 * @notice This is NatSpec
 * @param a This is NatSpec
 */
function foo(uint256 a) internal { }