[ADD/WIP] Start making string splitters

I want to go on an encore of XEP-0393, with _rectangles_ as boundaries,
this time.

src/include/StringSplit.h

@@ -0,0 +1,35 @@
+#ifndef PARSEE_STRINGSPLIT_H
+#define PARSEE_STRINGSPLIT_H
+
+#include <stdlib.h>
+
+/* Represents a boundary in a linesplit string */
+typedef struct StringRect {
+    char **source_lines;
+
+    /* NOTE: All of these values are inclusive */
+
+    /* The start line/character index */
+    size_t start_line;
+    size_t start_char;
+
+    /* The end line/character index */
+    size_t end_line;
+    size_t end_char;
+} StringRect;
+
+/** Splits a string into a set of NULL-terminated substrings, which is 
+ * terminated by a NULL pointer.
+ * ---------
+ * Returns: A set of lines(excluding them) [LA:HEAP]
+ * Modifies: NOTHING
+ * Thrasher: StrFreeLines */
+extern char ** StrSplitLines(char *text);
+extern void StrFreeLines(char **split);
+
+extern size_t StrLines(char **split);
+
+/* Creates a full zone covering every part of the split */
+extern StringRect StrFullRect(char **split);
+
+#endif