fs: Prevent invalid directory links

A file with a name like "gemini:example" would previously result in the
following invalid link:

    => gemini:example gemini:example

Fix by prepending a "./" before each filename, so that the resulting
link looks like:

    => ./gemini:example gemini:example

Fix parsing of list item lines

According to section 5.5.2 of the Gemini specification (v0.16.1), the
space is mandatory.

doc: Fix Mux documentation

readme: Update Gemini specification version

mux: Tweak documentation

mux: Add more tests

mux: Remove support for handling schemes

Also fix redirection to subtree roots for wildcard patterns and patterns
without a host name.

fs: Avoid equality check if lengths don't match

fs: Improve redirect behavior

fs: Refactor

fs: Remove ServeContent function

LoggingMiddleware: Prevent writing empty meta

fs: Fix panic on indexing URL of zero length

Update README.md

mux: Add copyright notice

Split LICENSE into two files

Revert "Require Go 1.16"

This reverts commit 0e87d64ffc2512563926d15cea6806f47205f7f9.

Revert "Replace uses of ioutil with io"

This reverts commit 19f1d6693ec85d4e3f83c3de2d4c366c8b612767.

response: Remove unnecessary length check

response: Limit response header size