test reading data with spaces

[twollnik]

closes #11

This PR modifies the existing test for the function readFiles. The files in the input directory now contain a lot of unnecessary spaces. The test makes sure that the input is read correctly despite all these unnecessary spaces.

• Add folder tests/testthat/test_data/no_spaces/ with isotope measurement files that do not contain spaces.
• Add spaces to csv files in folder tests/testthat/test_data/
• test compares the data read from the files with spaces to the data from the files without spaces.

@ikroener This is a very small PR and there is not much to review. I assigned it to you so that you can get the hang of things and decide if you want to be involved in more reviews in the future.

[twollnik]

Thanks for your comment and the helpful suggestion. I changed the spacing in one of the files to be less consistent. Merging this as soon as CI passes.