Relative base-URL is causing some confusion

[pwuertz]

Description

When using a relative base URL base-url = ".", the generated links from index.html to ./package/ are fine, but wheel-links within a subfolder like ./package/index.html still include the subfolder ./package/package-xyz.whl within the link, thus incorrectly referring to locations like package/package/package-xyz.whl.

Steps to Reproduce

Run simple503 . with simple503.toml:

[simple503]
base-url = "."
target = "."
sort = true
copy = false

Generated links to wheel files are off by one subfolder.

Actual result:

Generated links currently resolve to <base>/package/package/package-xyz.whl.

Expected result:

Generated links should resolve to <base>/package/package-xyz.whl.