Begin working on the lexer.

include/libabacus.h

@@ -0,0 +1,15 @@
+#ifndef LIBABACUS_H
+#define LIBABACUS_H
+
+/**
+ * An enum that represents the outcomes of
+ * libabacus functions that can fail.
+ */
+enum libab_result {
+    LIBAB_SUCCESS,
+    LIBAB_MALLOC
+};
+
+typedef enum libab_result libab_result;
+
+#endif