Improve print output for nested contexts

Example Output

```julia
AssocMatrix constructors
     - Simple Examples
     - Advanced Examples - Mixed Type Empty Arrays
       - All empty
       - Empty row
       - Empty value
       - Empty column and value
       - Empty row and value
     - Advanced Examples - Mixed Type Non-Empty Arrays
       - String Scalar, String Vector, Numeric Vector
       - Numeric Vector, String Vector, String Scalar
       - Numeric Vector, Numeric Scalar, String Scalar
       - String Scalar, Numeric Scalar, Numeric Scalar
       - String Scalar, String Scalar, Numeric Vector
       - String Scalar, String Scalar, Numeric Vector
       - String Scalar, Numeric Vector, Numeric Vector
15 facts verified.
```