add ELF data types

lib/elf/README.md

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+# Executable and Linkable Format (ELF)
+
+## References:
+1. https://en.wikipedia.org/wiki/Executable_and_Linkable_Format
+2. https://gabi.xinuos.com/
+3. https://github.com/xinuos/gabi

lib/elf/elf.h

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+/*
+ * REF: https://gabi.xinuos.com/elf/01-intro.html
+ */
+
+#include <stdint.h>
+
+/* Byte alignment for the ELF data types will always match the size.
+ * For example a structure containing an Elf32_Addr member will
+ * be aligned on a 4-byte boundary within the file.
+ */
+/* 32-Bit Data Types */
+typedef uint32_t Elf32_Addr;  /* Unsigned program address */
+typedef uint32_t Elf32_Off;   /* Unsigned file offset */
+typedef uint16_t Elf32_Half;  /* Unsigned medium integer */
+typedef uint32_t Elf32_Word;  /* Unsigned integer */
+typedef  int32_t Elf32_Sword; /* Signed integer */
+/* 64-Bit Data Types */
+typedef uint64_t Elf64_Addr;   /* Unsigned program address */
+typedef uint64_t Elf64_Off;    /* Unsigned file offset */
+typedef uint16_t Elf64_Half;   /* Unsigned medium integer */
+typedef uint32_t Elf64_Word;   /* Unsigned integer */
+typedef  int32_t Elf64_Sword;  /* Signed integer */
+typedef uint64_t Elf64_Xword;  /* Unsigned long integer */
+typedef  int64_t Elf64_Sxword; /* Signed long integer */
+
+