Read excluded directories from the `.gitignore` file of the repository (

CouscousPHP#165)

This allows users to have their git ignored files and directories automatically
ignored by Couscous. To enable this feature, they will have to add the special
`%gitignore%` entry to their exclude list.

Why do we use a special entry? To keep the actual behavior unchanged and avoid
unexpected generation errors.

The actual implementation is a bit naïve: it will take each entry line from the
`.gitignore` and add them to the exclude list of Couscous. So we might end up
adding files and directories. It's hard to test every `.gitignore` entry to see
if the are actual directories: paths might be relative or patterns, starting
from the repository's root directory or not.

Moreover, the implementation does not support complex pattern as git would.

Makes default pages boxed instead of full-width (CouscousPHP#164)

CouscousPHP#156 Add Markdown tests

Merge pull request CouscousPHP#144 from CouscousPHP/analysis-8m4rx1

Applied fixes from StyleCI

CouscousPHP#140 fixes

Merge pull request CouscousPHP#130 from mpodolian/bug/set-default-tim…

…ezone-119

Add a configuration step to check that the default timezone is set

Fix template's Markdown files overriding the project's Markdown files…

… when generating

Add instructions for releasing a new version

Removed the changelog since it's not up to date

See https://github.com/CouscousPHP/Couscous/releases instead

Merge CouscousPHP#101 manually