Closes #773

* zola init works without argument (defaults to current directory)

* zola init works with existing folders (no non-hidden files permitted)

* Update zola init documentation

* [docs] Optional argument is on a separate line for clarity

* Add tests for init subcommand's respect of existing folders

Closes #766

* 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.

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

* Mention serve --open flag in CLI documentation

* Update cli-usage.md

* clarify that it's only the links from markdown files that are being checked;

Close #686

* 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

This reverts commit 1815155c1d.

Closes #530

Fix #616. Add brief documentation for how to use it.

This reverts commit 5fd7bf7e61.

Apparently it is not just no longer necessary to use classic
confinement, but actually impossible, i.e. snap emits an error that the
zola snap is not compatible with `--classic`.

690b3f9 updated the required version in Cargo.lock and in the CI config files, but not in the installation instructions.

If you don't install with classic confinement, you'll get permission errors trying to create sites with `zola init`.

Changed arch linux from h2 to h3

I updated the install instructions (snap, scoop, chocolatey) and added the ones where Gutenberg already got renamed to Zola also to the top of the document.

Should yaourt be replaced by one of the other aur-helpers (pikaur, yay,...) as the development for it is stalled/discontinued for quite some time now although it is still working?

Scoop: https://github.com/lukesampson/scoop/blob/master/bucket/zola.json
Chocolatey: https://chocolatey.org/packages/zola
Snap: https://snapcraft.io/zola

Switch to an `Option<usize>` for the serialized value of `rss_items`.
This lets us just set a blank value in the configuration and thereby
include *all* items.

This is a backwards-compatible change; it does not affect the behavior
of existing configurations.

Fixes #468. Closes #471.

- unless forced, only use colors in tty
- support CLICOLOR and NO_COLOR vars
- switch to termcolor crate to handle output coloring

Close #115