Describe column name case insensitivity in metadata tutorial

[AmandaBirmingham]

Improvement Description
Extend the metadata tutorial to explicitly note that non-id column names must differ by more than just case. See reference 1 below.

Current Behavior
Currently, the Metadata class allows instantiation with inputs containing column names that differ only by case, but this leads to an error if using the get_ids() method.

Proposed Behavior
Add a sentence to the metadata.rst tutorial. My suggestion is to modify

docs/source/tutorials/metadata.rst

Line 110 in 8510b64

- Must be unique (exact string matching is performed to detect duplicates).

to

 - Must be unique without regard to case (e.g., columns `foo` and `Foo` in the same file are not allowed)

References

1. https://forum.qiime2.org/t/are-non-sample-id-column-names-case-insensitive-in-metadata-files/29508

[hagenjp]

Hi @AmandaBirmingham, we are looking into a solution for this one and its not as simple as we thought because this is not an intentional behavior within qiime2. I think we will want to find a better solution than just changing documentation. Many thanks for bringing this one to our attention!