Add support for Variable Case Standardization

[TaoK]

In a tweet, Brent Ozar notes that there's no option to standardize variable names in a script, eg take the first instance (/declaration) of @Id and change any subsequent references to "@ID", "@iD", or "@id" to match:

https://twitter.com/BrentO/status/828626157411172353

A naive implementation of this (not worrying about variable scope / batch separators but simply assuming that you want the same case even across batches) should be pretty easy to implement. On the pile it goes!