SMD_matrix improvements

[Deleetdk]

Should add some things:

1. Option to get CIs on the values like cor_matrix. Standard and bootstrapped (when using non-parametric).
2. Why is this called _matrix and gives matrix (2x2) output when it only takes in one pair of variables? Because the group variable may have more than 2 levels. However, in the case of only 2 levels, it makes sense to simplify the output to a single value. Toggleable by argument otherwise the function would be unpredictably output type inconsistent.
3. Option to get the CIs in separate matrices for easy computational re-use.
4. Throw error when given length 1 input. Right now this just results in no errors and NA output. Confusing!

[Deleetdk]

Re. 2. Keep it as it is.

[Deleetdk]

5. Add options to input reliabilities to adjust for measurement error.

Is there a better way to do this than converting to correlations and back?

[Deleetdk]

Re. 5. Seems not, but there's now a function to do this: a4me_cohen_d (adjust for measurement error).

e771800

[Deleetdk]

Option to get the CIs in separate matrices for easy computational re-use.

This one came up again and I needed to use CIs in a function, so now's the time to implement this.

Adding the options to change the input to a list would be in semi-conflict with Hadley's principle of output consistency. This one however is not due to any behind the scenes conditions, but a parameter, so it's more okay.