Adding string processing

- 'character' type, only contructible by decomposing strings
- 'boom' builtin function ;) to create a list of characters from a string
- string library with basic manipulation functionalities
- slightly improved Makefile

Makefile

@@ -1,17 +1,23 @@
 default: build-release
 
 build-release:
-	cargo build --release
+	@echo "Build release"
+	@cargo build --release
 
 test:
-	cargo test --release
+	@echo "Test release"
+	@cargo test --release
 
 conf:
-	mkdir -p ${HOME}/.config/mal
+	@echo "Copy core and libraries"
+	@mkdir -p ${HOME}/.config/mal
 	cp -f core/core.mal ${HOME}/.config/mal/
-	mkdir -p ${HOME}/.config/mal/libs
+	@mkdir -p ${HOME}/.config/mal/libs
 	cp -f libs/* ${HOME}/.config/mal/libs/
 
 install: build-release test conf
+	@echo "Install mal"
 	sudo cp target/release/rust-mal /usr/local/bin/mal
-	sudo chown ${USER} /usr/local/bin/mal
+	@sudo chown ${USER} /usr/local/bin/mal
+	@echo "To start mal run:"
+	@printf "\tmal [path/module.mal ...]\n\n"