Implemented the following attributes:

* String.length
* String.asUpper
* String.asLower
* array.length
* array.pushBack(x)
* array.popBack()

The remaining attributes are listed in 'toy_attributes.h'

tests/units/test_attributes.c

@@ -0,0 +1,9 @@
+#include "toy_console_colors.h"
+
+#include <stdio.h>
+#include <string.h>
+
+int main(void) {
+	printf(TOY_CC_WARN "Test not yet implemented: %s\n" TOY_CC_RESET, __FILE__);
+	return 0;
+}