allow notebook as hidden dir

[tjex]

resolves: #271

The index function of zk calls a directory walk. That walk function was set to ignore all directories and files that had a period as a prefix. This applied then to the notebook root directory itself. This also effected commands such as zk list.

This fix is an initial approach to solving that by checking if the directory begins with a prefix and the directory in question does not equal the notebook root directory.

This equality check is done by getting the notebook directory from the NotebookPath.Filename() method, and checking it against the value of filename in internal/util/paths/walk.go.

Note: It was not possible to import the core package to walk.go as it created an import cycle. This is why it is instead accessed in internal/core/note_index.go line 153 and passed to the paths.Walk() call.

On that line (153), I'm unsure whether I've used the NotebookPath struct correctly as in other areas of the code base, all fields of the struct are declared.

I have however tested this fix with success. That being a notebook with root dir .test-vault; zk indexes and lists correctly, meaning it ignores the .zk and .git directories as well as a .test-file.md note created via zk.

Please let me know if there is a better way to do this! 🙏

[jurica]

@tjex I have one little nitpick.
Regarding your issue with the cyclic reference: IMHO it's perfectly fine to add that new argument to Walk.