Hi,

I've had to make another update to the general publications support code in order to implement a feature of the SBL rendering. Denis Maier has opened some issues on the context-sbl GitHub repo (https://github.com/jjmccollum/context-sbl) to offer some helpful suggestions about needed features and bug fixes. One issue was that SBL should order list entries by author and title. Thankfully, there is already an authordate sortmethod defined in publ-aut.lua (probably to support the Chicago rendering), so I was able to use it as a template for the following authortitle sort sequence:

```
publications.sortmethods.authortitle = {
    sequence = {
        { field = "author",  default = "",     unknown = "" },
        { field = "title",   default = "",     unknown = "" },
        { field = "date",  default = "9998-13-32",     unknown = "9999-14-33" }, -- some specifications allow date instead of year, month, day
        { field = "year",    default = "9998", unknown = "9999" },
        { field = "month",   default = "13",   unknown = "14" },
        { field = "day",     default = "32",   unknown = "33" },
        { field = "index",   default = "",     unknown = "" },
    },
}
```

I added this to publ-aut.lua because publications.sortmethods.authoryear is defined in that file, but if another location is more appropriate, then feel free to let me know, and I can move it! Otherwise, if this looks okay to include in a future update, then feel free to incorporate it!

Joey