extension.selectBackTick support for markdown code chunks ```

[mkoohafkan]

R Markdown and Python Markdown documents often contain runnable code chunks with the following format:

```{r chunk-name, opt1 = "something", opt2 = "something-else"}
# some code
```

Currently, the extension.selectBackTick includes the code chunk specifications, i.e. everything inside the curly braces {}. It would be great if there were an option to also exclude the code chunk specification, or provide a extension.selectTripleBackTick method to handle this.