Merge branch 'makefiles-and-ci' into 'master'

Update project files for linux and add CI

See merge request clean-and-itasks/clean-ide!3

.gitignore

+cpm/cpm
+Clean System Files

.gitlab-ci.yml

+test:
+    before_script:
+        - install_clean_nightly.sh bundle-complete
+        - apt-get update -qq
+        - apt-get install -y -qq build-essential
+    image: "camilstaps/clean:nightly"
+    script:
+        - clm -nt -nr -h 67108864 -s 5242880 -IL ArgEnv -IL StdLib -IL Directory -I Pm -I Unix -I Util -I BatchBuild -I Interfaces/LinkerInterface -I cpm/Posix -I cpm Cpm -o cpm/cpm
+        - cpm CpmLinux.prj --force
+    artifacts:
+        paths:
+            - "cpm/cpm"

README.md

+# clean-ide
+
+This contains the Windows IDE, batchbuild and cpm.
+
+## Automatic builds
+
+cpm is included in all clean distributions. However, if you cannot wait for the
+nightly build you can download one of the automatic builds here:
+
+- [linux-64](https://gitlab.science.ru.nl/clean-and-itasks/clean-ide/builds/artifacts/master/file/cpm/cpm?job=test)