Function `query_row` executes query and calls callback function to process
row returned. Function query_row_col() is special case, that provides
callback function, which returns value of one particular column of row,
ignoring others.
In all cases, that particular column was 0 (first and only column of
query result), since there is no point to select more than one column
with this function -- they are discarded anyway.
This commit removes that redundancy, removing column number argument of
query_row_col() function and adjusting call sites accordingly.
* 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.
