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new functions added

char charAt(long index); //return character at the given index, NULL
(\0) for invalid index.
char * get(void);   //get the content.
bool isPalindrome(void); //true (1) if string is Palindrome. false (0)
otherwise.
long indexOf(const char ch);  //return index of first occurance of the
character ch in string, -1 otherwise.
long indexOf(const char *str);  //return index of first occurance of the
substring str in string, -1 otherwise.
void insertAt(const char ch, long index); //insert character ch at
position index in string when index is valid, ignore otherwise.
long lastIndexOf(const char ch); //return index of last occurance of the
character ch in string, -1 otherwise.
long lastIndexOf(const char *str); //return index of last occurance of
the substring str in string, -1 otherwise.
long length(void);   //length of the string.
void replace(const char ch, const char nch); //replace all occurance of
the character ch with nch in the string.
void reverse(void);   //reverse string.
void toggleCase(void);  //toggle case. convert A to a and vice-versa.
void toUpper(void);   //to upper case. convert a to A.
void toLower(void);   //to lower case. convert A to a.
void trim(void);   //remove space from front and end of the string.
char * substring(long start); //return a substring from index start till
end of the string, for invalid start index return NULL (\0)
char * substring(long start, long end); //return a substring from index
start to end both inclusive, for invalid index return NULL (\0)
functions implementation