Makefile:
Move shellcheck to a "lint" target and change "check" so that it runs "lint".
This provides a more finer grained control and allows to extend "check" with things beyond just linting.

.gitlab-ci.yml:
Run `make lint` in the lint job.

LICENSE:
Add GPL-3.0 license.

{{archiso,configs}/*,.editorconfig,.gitlab-ci.yml}:
Add SPDX license identifier.

Makefile:
Add SPDX license identifier.
Install the `run_archiso.sh` script as global executable `run_archiso`.
Use -D and -t flags to install to install files more generically (without a previous call to install the directory).

README.rst:
Add README outlining the project's scope, how to build images from the profiles and how to test.

AUTHORS.rst:
Add list of all direct contributors to the repository.

CONTRIBUTING.rst:
Add basic contribution guidelines, explaining the linter and the license in use.

Closes #7
Closes #3

Makefile:
Move shellcheck commands from .gitlab-ci.yml.

.gitlab-ci.yml:
Run `make check`.
Prevent partial upgrades, i.e. use '-Syu'.
Prevent reinstalling already installed packages by using pacman's '--needed' option.
Don't force-download the package database.

archiso/initcpio/install/*:
Setting bash shebang for all scripts and making them comform with shellcheck.

archiso/initcpio/{hooks,script}/*:
Setting ash shebang for all scripts and making them comform with shellcheck (for dash, as shellcheck has no ash specific
ruleset). Essentially the ash based scripts should be POSIX compliant as much as possible to have an easier time
writing, debugging and maintaining them.
Ensuring that variables are not treated as options and introducing variable quoting.

.gitlab-ci.yml:
Integrating shellcheck for initcpio scripts.

Closes #32

scripts/run_archiso.sh:
A script to run a built archiso image using qemu.
It can run the image on an emulated BIOS (using seabios) or UEFI (using edk2-ovmf) system.

.gitlab-ci.yml:
Adding scripts/run_archiso.sh to shellcheck call.

Closes #28

/etc/systemd/scripts/ is not a standard directory.

Run shellchek on the choose-mirror script.

archiso/mkarchiso:
Quoting all variables.
Changing pkg_list to be an array instead of a string for easier
handling. Using read to properly populate pkg_list from OPTARG with
stripped whitespaces.
Not exporting iso_label anymore as there seems to be no reason to do so.
Introducing line breaks.

.editorconfig:
Setting max_line_length to 120.
Adding a section for YAML files (e.g. .gitlab-ci.yml).

configs/releng/build.sh
Quting nearly all variables.
Introducing line breaks.

configs/baseline/build.sh:
Quoting all variables.
Introducing line breaks.

.gitlab-ci.yml:
Adding gitlab CI for shelleck linting of the config build scripts, mkarchiso and startup scripts in releng.

Closes #19