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: Remove ServeContent function
LoggingMiddleware: Prevent writing empty meta
fs: Fix panic on indexing URL of zero length
mux: Add copyright notice
Split LICENSE into two files
Revert "Replace uses of ioutil with io"

This reverts commit 19f1d6693ec85d4e3f83c3de2d4c366c8b612767.
response: Remove unnecessary length check
response: Limit response header size