* cargo fmt & clippy

* Skip anchor checking for URL with prefix in config

* Let toc is visable through Page & Section variables in templates

* Removed the current toc variable from page & section

Links that start with a scheme (e.g., `tel:18008675309`) inadvertently
had a URL prefix prepended. Previously, only `mailto:` was handled, but
given the sheer number of [registered URI schemes][uri-schemes], a loose
pattern matcher is used to detect schemes instead.

External links, as identified by the renderer, are now limited to `http`
and `https` schemes.

Fixes #747 and fixes #816.

[uri-schemes]: https://www.iana.org/assignments/uri-schemes/uri-schemes.xhtml

* 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

The access to translations is not straightforward and requires checks if
language and key exists. It is better to forbit direct access to
attribute and provide method - `get_translation()` - that will handle
all details of key translations.

Remove unit tests that use direct access and test only public method.

* fix the issue of generating the search index for multiple language

* updat docs for generating the search index for multiple language

* fix failed tests

* add tests for the search index of multiple language

Add method get_translation(lang, key) into Config struct that retrieves
translated term from parsed configuration or error when either
desired language or key is missing.

Use the new method in Trans struct implementing global Tera function
trans().

Add unit test to cover both happy and error path for translation
retrieval in both config and templates crate.

* Fix the issue when checking the changes of multiple language section

Closes #790

* Fix ToC generation for heading levels > 3

* typo

* Add tests for deep ToCs

* Code style change

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

Closes #733

Closes #766

Closes #719

* Allow ignored_content to support markdown files

* Add test for markdown supported ignored_content

These functions expect that file_path can have base_path stripped from
it, but during reloading they can be given relative paths.  Maybe this
behaviour varies between the notify backends?

This fixes two zola serve panics on FreeBSD (poll backend).

Closes #756

* Set up CI with Azure Pipelines

[skip ci]

* Remove other CI + remove newline in anchor link tpl

* Some more Windows specific changes

Closes #726

Part fix of #742

Clippy is returning some warnings.  Let's fix or explicitly ignore
them.  In particular:

- In `components/imageproc/src/lib.rs`, we implement `Hash` explicitly
  but derive `PartialEq`.  We need to maintain the property that two
  keys being equal implies the hashes of those two keys are equal.
  Our `Hash` implementations preserve this, so we'll explicitly ignore
  the warnings.

- In `components/site/src/lib.rs`, we were calling `.into()` on some
  values that are already of the correct type.

- In `components/site/src/lib.rs`, we were using `.map(|x| *x)` in
  iterator chains to remove a level of indirection; we can instead say
  `.copied()` (introduced in Rust v1.36) or `.cloned()`.  Using
  `.copied` here is better from a type-checking point of view, but
  we'll use `.cloned` for now as Rust v1.36 was only recently
  released.

- In `components/templates/src/filters.rs` and
  `components/utils/src/site.rs`, we were taking `HashMap`s as
  function arguments but not generically accepting alternate `Hasher`
  implementations.

- In `src/cmd/check.rs`, we use `env::current_dir()` as a default
  value, but our use of `unwrap_or` meant that we would always
  retrieve the current directory even when not needed.

- In `components/errors/src/lib.rs`, we can use `if let` rather than
  `match`.

- In `components/library/src/content/page.rs`, we can collapse a
  nested conditional into `else if let ...`.

- In `components/library/src/sorting.rs`, a function takes `&&Page`
  arguments.  Clippy warns about this for efficiency reasons, but
  we're doing it here to match a particular sorting API, so we'll
  explicitly ignore the warning.

* Add hard_link_static config option.

* Copy or hardlink file depending on an argument.

Modify the call sites for `copy_file` to account for the extra argument.

* Plug the config setting through to copy_file.

Don't apply the config option to theme's static directory.

* Update documentation.

* Backticks make no sense in this comment.

* Addressing PR comments.

* Be consistent with argument naming.

Closes #722

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

Without this, at least one search engine spider was generating a
validation warning.