Custom glue delimiters. Small bug fix literal braces with parseable braces.

[radbasa]

Closes #100

Description

• Provides customizable opening and closing delimites for glue strings. This is done via options(). Most user-friendly method for setting custom delimiters. There are 5 linter functions that work with glue strings.
• Small bug fix for "Some {{literal}} and {value} strings." not finding value.

Definition of Done

• [ ] The change is thoroughly documented.
• [ ] The CI passes (R CMD check, linter, unit tests, spelling).
• [ ] Any generated files have been updated (e.g. .Rd files with roxygen2::roxygenise())

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 98.38%. Comparing base (309e858) to head (2b6acf5).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #101 +/- ## ========================================== + Coverage 98.37% 98.38% +0.01% ========================================== Files 21 21 Lines 799 804 +5 ========================================== + Hits 786 791 +5 Misses 13 13 ```

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