[Makefile] Modifies install/uninstall target. Adds help target (#135)

Makefile:

Install target:
- Added "uninstall" and "help" target to ".phony".
- Hook initcpio will be installed only on Arch Linux like distributions.

Uninstall target:
- All commands are in silent mode.
- "rmdir" command will not interrupt the uninstallation if the folder does not exist.
- Remove "-r" option to "rm" command.
- Fix a mistake in deleting the "readme" file.
- Uninstalling the "grub-btrfs.cfg" file uses the "GRUB_BTRFS_GRUB_DIRNAME" variable.
- Delete initcpio folder if not on Arch.
- Delete "grub-btrfs" docs and licenses folders.

help target:
- Add "help" target.

Makefile

@@ -4,28 +4,57 @@ PREFIX ?= /usr
 SHARE_DIR = $(DESTDIR)$(PREFIX)/share
 LIB_DIR = $(DESTDIR)$(PREFIX)/lib
 
-.PHONY: install
+.PHONY: install uninstall help
 
 install:
 	@install -Dm755 -t "$(DESTDIR)/etc/grub.d/" 41_snapshots-btrfs
 	@install -Dm644 -t "$(DESTDIR)/etc/default/grub-btrfs/" config
 	@install -Dm644 -t "$(LIB_DIR)/systemd/system/" grub-btrfs.service
 	@install -Dm644 -t "$(LIB_DIR)/systemd/system/" grub-btrfs.path
 	@install -Dm644 -t "$(SHARE_DIR)/licenses/$(PKGNAME)/" LICENSE
-	@install -Dm644 "initramfs/Arch Linux/overlay_snap_ro-install" "$(LIB_DIR)/initcpio/install/grub-btrfs-overlayfs"	# Arch Linux only
-	@install -Dm644 "initramfs/Arch Linux/overlay_snap_ro-hook" "$(LIB_DIR)/initcpio/hooks/grub-btrfs-overlayfs"		# Arch Linux only
+	@# Arch Linux like distros only :
+	@if command -V mkinitcpio >/dev/null 2>&1; then \
+		install -Dm644 "initramfs/Arch Linux/overlay_snap_ro-install" "$(LIB_DIR)/initcpio/install/grub-btrfs-overlayfs"; \
+		install -Dm644 "initramfs/Arch Linux/overlay_snap_ro-hook" "$(LIB_DIR)/initcpio/hooks/grub-btrfs-overlayfs"; \
+	 fi
 	@install -Dm644 -t "$(SHARE_DIR)/doc/$(PKGNAME)/" README.md
 	@install -Dm644 "initramfs/readme.md" "$(SHARE_DIR)/doc/$(PKGNAME)/initramfs-overlayfs.md"
 
 uninstall:
-	rm -f "$(DESTDIR)/etc/grub.d/41_snapshots-btrfs"
-	rm -f "$(DESTDIR)/etc/default/grub-btrfs/config"
-	rm -f "$(LIB_DIR)/systemd/system/grub-btrfs.service"
-	rm -f "$(LIB_DIR)/systemd/system/grub-btrfs.path"
-	rm -f "$(SHARE_DIR)/licenses/$(PKGNAME)/LICENSE"
-	rm -f "$(DESTDIR)/boot/grub/grub-btrfs.cfg"
-	rm -f "$(LIB_DIR)/initcpio/install/grub-btrfs-overlayfs" # Arch Linux only
-	rm -f "$(LIB_DIR)/initcpio/hooks/grub-btrfs-overlayfs" # Arch Linux only
-	rm -rf "$(SHARE_DIR)/doc/$(PKGNAME)/" README.md
-	rm -rf "$(SHARE_DIR)/doc/$(PKGNAME)/initramfs-overlayfs.md"
-	rmdir --ignore-fail-on-non-empty "$(DESTDIR)/etc/default/grub-btrfs"
+	@grub_dirname="$$(grep -oP '^[[:space:]]*GRUB_BTRFS_GRUB_DIRNAME=\K.*' "$(DESTDIR)/etc/default/grub-btrfs/config" | sed "s|\s*#.*||;s|(\s*\(.\+\)\s*)|\1|;s|['\"]||g")"; \
+	 rm -f "$${grub_dirname:-/boot/grub}/grub-btrfs.cfg"
+	@rm -f "$(DESTDIR)/etc/default/grub-btrfs/config"
+	@rm -f "$(DESTDIR)/etc/grub.d/41_snapshots-btrfs"
+	@rm -f "$(LIB_DIR)/systemd/system/grub-btrfs.service"
+	@rm -f "$(LIB_DIR)/systemd/system/grub-btrfs.path"
+	@rm -f "$(LIB_DIR)/initcpio/install/grub-btrfs-overlayfs"
+	@rm -f "$(LIB_DIR)/initcpio/hooks/grub-btrfs-overlayfs"
+	@# Arch Linux unlike distros only :
+	@if ! command -V mkinitcpio >/dev/null 2>&1; then \
+		rmdir --ignore-fail-on-non-empty "$(LIB_DIR)/initcpio/install" || :; \
+		rmdir --ignore-fail-on-non-empty "$(LIB_DIR)/initcpio/hooks" || :; \
+		rmdir --ignore-fail-on-non-empty "$(LIB_DIR)/initcpio" || :; \
+	 fi
+	@rm -f "$(SHARE_DIR)/doc/$(PKGNAME)/README.md"
+	@rm -f "$(SHARE_DIR)/doc/$(PKGNAME)/initramfs-overlayfs.md"
+	@rm -f "$(SHARE_DIR)/licenses/$(PKGNAME)/LICENSE"
+	@rmdir --ignore-fail-on-non-empty "$(SHARE_DIR)/doc/$(PKGNAME)/" || :
+	@rmdir --ignore-fail-on-non-empty "$(SHARE_DIR)/licenses/$(PKGNAME)/" || :
+	@rmdir --ignore-fail-on-non-empty "$(DESTDIR)/etc/default/grub-btrfs" || :
+
+help:
+	@echo
+	@echo "Usage: $(MAKE) [ <parameter>=<value> ... ] [ <action> ]"
+	@echo
+	@echo "  actions: install"
+	@echo "           uninstall"
+	@echo "           help"
+	@echo
+	@echo "  parameters | description                    | defaults"
+	@echo "  -----------+--------------------------------+----------------------------"
+	@echo "  DESTDIR    | install destination            | <unset>"
+	@echo "  PREFIX     | system tree prefix             | '/usr'"
+	@echo "  SHARE_DIR  | shared data location           | '\$$(DESTDIR)\$$(PREFIX)/share'"
+	@echo "  LIB_DIR    | system libraries location      | '\$$(DESTDIR)\$$(PREFIX)/lib'"
+	@echo "  PKGNAME    | name of the ditributed package | 'grub-btrfs'"
+	@echo