Certain tests involving HTTP requests were sometimes hanging
indefinitely, so this uses Mockito for HTTP mocking. This seemingly
resolves the issue and makes these tests more reliable.

The existing can_fail_404_links test has been renamed to
can_fail_unresolved_links, to represent what actually occurs in the
test. The can_fail_404_links test now deals with a proper 404
response.

Just to be clear, the check_site test in the site component will
still create outgoing HTTP requests (due to the URLs used in the
test_site), so this commit only uses HTTP mocking where possible.

* maybe_slugify() only does simple sanitation if config.slugify is false

* slugify is disabled by default, turn on for backwards-compatibility

* First docs changes for optional slugification

* Remove # from slugs but not &

* Add/fix tests for utf8 slugs

* Fix test sites for i18n slugs

* fix templates tests for i18n slugs

* Rename slugify setting to slugify_paths

* Default slugify_paths

* Update documentation for slugify_paths

* quasi_slugify removes ?, /, # and newlines

* Remove forbidden NTFS chars in quasi_slugify()

* Slugification forbidden chars can be configured

* Remove trailing dot/space in quasi_slugify

* Fix NTFS path sanitation

* Revert configurable slugification charset

* Remove \r for windows newlines and \t tabulations in quasi_slugify()

* Update docs for output paths

* Replace slugify with slugify_paths

* Fix test

* Default to not slugifying

* Move slugs utils to utils crate

* Use slugify_paths for anchors as well

Closes #866

* cargo fmt & clippy

* Skip anchor checking for URL with prefix in config

* Bump pulldown_cmark to version 0.6.0

* Rename headers to headings

* Add anchor existant checking to link_checker component

* Oops, forgot some changes

* Drop scraper dependency and rework tests

* Handle name attributes

Closes #790

>3.2.0 has an updated onig version which requires llvm
which isn't built in azure pipelines in Windows

Closes #766

Closes #719

Part fix of #742

* Add --open flag to serve command, to open URL in default browser

* Mention serve --open flag in CLI documentation

Signed-off-by: Igor Gnatenko <i.gnatenko.brain@gmail.com>

* actix_web::fs is now found in the actix-files crate.

* NotFoundHandler is now implemented using ErrorHandlers and the
path to 404.html is provided to the not_found() function using
actix_web::App::data. This setup allows for additional StatusCodes
to be handled in the future, if desired.

* Cleanly serving index.html files for requests to directories now
appears to be possible simply by using index_file("index.html") in
the static files service, so handle_directory() is removed.

* chore: Update glob to 0.3

Signed-off-by: Igor Gnatenko <i.gnatenko.brain@gmail.com>

* chore: Update ws to 0.8

Signed-off-by: Igor Gnatenko <i.gnatenko.brain@gmail.com>

Close #693

* Add check subcommand

* Add some brief documentation for the check subcommand

* Start working on parallel link checks

* Check all external links in Site

* Return *all* dead links in site