This regression seems more severe than the bug the commit was
attempting to fix (incorrect parsing of nested wikilinks in normal
links), so that bug is reintroduced until localization-aware parsing
that allows us to detect file links is added.

This commit partially reverts fac60dee48.

Signed-off-by: odidev <odidev@puresoftware.com>

* Proposed fix for https://github.com/earwig/mwparserfromhell/issues/197

* Port the fix for #197 to the C tokenizer

* Fix parsing of external links where the URL is terminated by some special character

- One existing test case has been found wrong -- current MediaWiki
  version always terminates the URL when an opening bracket is
  encountered.
- Other test cases added: double quote, two single quotes and angles
  always terminate the URL (regardless if it is a free link or external
  link inside brackets). One single quote does not terminate the URL.

* Fix case-insensitive parsing of URI schemes

It's EOL and AppVeyor builds are broken under it if we want to support Python 3.9.

Not fully deprecating 3.5 for now because it's still used on Toolforge.

Fixes #198

Co-authored-by: Ben Kurtovic <ben.kurtovic@gmail.com>