Add ET_DYN support for the ELF loader, which required adding

relocations, add some more functions to libxunil, use include inside of
tests instead of manually defining types and add basic libc header
files. Move libxunil to the user folder, and add helloworld and
doomgeneric as apps

user/libxunil/include/stdio.h

@@ -0,0 +1,32 @@
+#pragma once
+#include <stddef.h>
+#include <stdarg.h>
+
+typedef struct FILE FILE;
+
+extern FILE *stdin;
+extern FILE *stdout;
+extern FILE *stderr;
+
+#define EOF (-1)
+
+FILE  *fopen(const char *path, const char *mode);
+int    fclose(FILE *fp);
+size_t fread(void *ptr, size_t size, size_t nmemb, FILE *fp);
+size_t fwrite(const void *ptr, size_t size, size_t nmemb, FILE *fp);
+int    fseek(FILE *fp, long offset, int whence);
+long   ftell(FILE *fp);
+int    fflush(FILE *fp);
+char  *fgets(char *s, int size, FILE *fp);
+int    fputs(const char *s, FILE *fp);
+int    feof(FILE *fp);
+int    ferror(FILE *fp);
+
+int    printf(const char *fmt, ...);
+int    fprintf(FILE *fp, const char *fmt, ...);
+int    sprintf(char *buf, const char *fmt, ...);
+int    snprintf(char *buf, size_t size, const char *fmt, ...);
+int    vsnprintf(char *buf, size_t size, const char *fmt, va_list ap);
+int    vfprintf(FILE *fp, const char *fmt, va_list ap);
+void write(int fd, const char* buf, unsigned long count);
+void exit(int code);