string operation

basic operation of string, including strcat, strcpy, strStr, strcmp,
strlen, reverse_str, str_shift, longest palindrome using manacher
method, and implentation of String class
Revert "string operation"

This reverts commit fa60fcafed56e53d8f4dedf3aef73617ea1a577e.
string operation modify
Merge pull request #16 from JimberXin/master

string operation