Add simpler method for test generation

[zbreit]

While generating test code for C and C++, I found that manually specifying WordLocations was quite tedious. It made it challenging to add new test cases when testing new language features.

To simplify this process, this commit adds the get_marked_misspellings() function, which takes in an input string where all expected misspellings are marked using start/end delimiters. The function returns a struct containing:

1. The input string with the delimiters removed.
2. All of the marked misspellings.

You can use this function to quickly test lots of functionality using simple-to-create input files.

As an example, I converted the C-language tests to use this new functionality. As a result of the testing, I identified and fixed a bug related to enum, struct, and union specifiers. Previously, codebook would flag Structt, Enumm and Unionn in the following code snippet:

   struct Structt a;
   enum Enumm a;
   union Unionn a;

[zbreit]

Wasn't sure what you thought of this approach, but I think it makes writing tests a bit easier. Let me know if you have any suggestions!