Make TemplateConfig fields public to avoid "cannot access private field" error

[gechandesu]

Since V 0.4.6 accessing to private fields produces an error e.g.:

 FAIL  [1/4] C:   735.4 ms, R:     0.000 ms /home/ge/Code/whisker/spec/spec_test.v
>> compilation failed:
spec/spec_test.v:21:43: error: cannot access private field `input` on `template.TemplateConfig`
   19 |         for test in suite.tests {
   20 |             println('${suite.name}: ${test.name}')
   21 |             spec_template := template.from_strings(input: test.template, partials: test.partials)!
      |                                                    ~~~~~~~~~~~~~~~~~~~~
   22 |             output := spec_template.run(test.data)!
   23 |             // dump(output)
spec/spec_test.v:21:65: error: cannot access private field `partials` on `template.TemplateConfig`
   19 |         for test in suite.tests {
   20 |             println('${suite.name}: ${test.name}')
   21 |             spec_template := template.from_strings(input: test.template, partials: test.partials)!
      |                                                                          ~~~~~~~~~~~~~~~~~~~~~~~
   22 |             output := spec_template.run(test.data)!
   23 |             // dump(output)

this commit fixes it.

Checklist

• The project compiles with v . and v -prod ..
• The unit tests are passing with v test .
• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• There exists a corresponding issue as a Bug Report or a
  Feature Request.
• (Optional) I have contacted the developers and received
  feedback on the aforementioned issue.