Length prefixed C strings, length is at the start of the allocated memory

e.g :
-----------------------------------------------
| 0 | 0 | 0 | 4 | 'T' | 'E' | 'S' | 'T' | '\0'|
-----------------------------------------------
                ^
              return
User can keep pointer to first character, so it's like C style strings with
additional functionality.

• User gets a null terminated char*, so it still works with c style string
  functions, e.g printf, strcmp.
• Faster length access and copy.
• Provides a few more functions to make easier create/append/trim/substring
  operations.

• 4 bytes fixed overhead per string.
• When you create/set/append a string, new memory is allocated. If you are
  modifying strings a lot, consider using buffer-like implementation for that if
  performance is critical for your use-case. I modify strings rarely but access
  a lot (copy/move etc.).

#include "sc_str.h"

#include <stdio.h>

int main(int argc, char *argv[])
{
    char* s1;

    s1 = sc_str_create("*-hello-*");
    printf("%s \n", s1); // prints *-hello-*

    sc_str_trim(&s1, "*-");
    printf("%s \n", s1); // prints hello

    sc_str_append_fmt(&s1, "%d", 2);
    printf("%s \n", s1); // prints hello2

    sc_str_replace(&s1, "2", " world!");
    printf("%s \n", s1); // prints hello world!

    sc_str_substring(&s1, 0, 5);
    printf("%s \n", s1); // prints hello

    sc_str_destroy(s1);

    return 0;
}