Improve test suite automation

[westonganger]

It would be a huge improvement to the test suite if the tests validated the xml contents of the spreadsheets automatically instead of requiring a manual look at the test spreadsheets.

I would love any PR's or contributions that could help improve our tests. Some test examples to get started could be found within the axlsx repo.

[westonganger]

We started adding test suite automation in the latests PRs, also we have merged into caxlsx directly so tests must now adhere to the requirements stated on that repo.