Show HN: I rewrote few of the common core string.h functions

Summary

1 strlen() Returns the number of characters in the string, excluding the null terminator \0. 2 strcpy() Copies contents of src string to dest. 3 strcat() Appends src string to the end of dest. 4 strncat() Appends up to n characters from src to dest. 5 strcmp() Compares two strings and returns 0 if equal. 6 strcspn() Finds a character from a array of string 7 strerror() Returns the string description of an error code. 8 memchr() Returns a pointer to the first byte in a block of memory which contains a specified value