* refactor(contact): rename and rusty memory allocations
* refactor(contact): use enum to indidcate origin
* refactor(contact): safe blocking and unblocking api
* refactor(contact): only safe and no more cstrings
Add a trait for str.strdup() to replace to_cstring() which avoid the
signature ambiguity with .to_string().
Also instruduce CString::yolo() as a shortcut to
CString::new().unwrap() and use it whenever the variable does can be
deallocated by going out of scope. This is less error prone.
Use some Path.to_c_string() functions where possible.
