DigitSymbol separator requires both

[jpgoldberg]

Resolves #15

The external changes are that

1. A new pre-baked separator function, SFDigitsAndSymbols requires that at least one digit and at least one symbol appear as separators somewhere. Note that setting this for a pwd with only one separator will fail.

2. The two character separators are no more. (We will be able to bring them back, but it will take some work). I do not believe that anyone was using them or that we exposed those in any UI

3. This exports some new stuff (which needs to be reviewed)

In order to do (1), which is what the issue called for, I needed to change how the separator functions work and how they are used during password generation. So there is a lot of new code in here. This does look a bit ahead to other things which we would like to do with separators.

Note that I will be traveling a great deal over the summer and my availability is limited.

Concerns before merging

• [ ] Tests of constant separators
• [ ] Tests of proper entropy calculation when using the new separator functions
• [ ] Review of what should and shouldn't be exported
• [ ] Are there better ways to make use of the function type definitions to clean up code.