growthscreener 1.6.0

• This version improves consistency in sieves and messages
• Adds checks on missing data for z1 in some edge cases where needed
• Adds messages **24 and **25 for edge cases where the Z-score cannot be calculated, even if all information is available
• Adds a test_gain argument to all screening functions that we may use to disable any checking on gain scores z1 - z0 (e.g. when there is only one observation for a child)
• Uses stricter scalar comparison operators && and ||
• Makes SD and SDS consistent in messages
• Replaces text "voorlaatste" to the more generic "eerdere"
• Adds test code that runs all json files in jamestest