Add CI on push to main and whenever a pull_request is opened, reopened or synchronized

Jobs:

• Run npm test
• Lint with prettier to enforce code formatting

A yacc grammar may have the following

%union {
  int integer;
}

%type <integer> rule

The integer is a field in the semantic stack, and the %type indicates that the listed rule "returns" that field.

c-xrefactory doesn't understand the %type declaration so a rename of the field will miss that occurrence.