Check if given cache path makes sense

[manusimidt]

Describe the bug
A clear and concise description of what the bug is:

Not really a bug, but if the user forgets to add the / at the end of the cache path, the HttpCache will store the files in i.e: ./cachewww.sec.gov.

To Reproduce
Steps to reproduce the behavior:

Expected behavior
A clear and concise description of what you expected to happen:

Automatically append the / at the end of the cache path

Screenshots
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cache: HttpCache = HttpCache('./cache')
# should have the same effect as:
cache: HttpCache = HttpCache('./cache/')