Linear model input

• Accepts LinearModel objects as a y variable
• Accepts Table objects as a y variable
• Examples are now in standalone files
• Legacy call format removed
• x variable does not need to be defined as empty when it isn't being used

new input arg format

New features: add median to plots, choose SEM or t-interval, return stats as second output, use parameter/value pairs by default and warn user if they aren't doing this. Add unit tests.