message: Add `function_rename` api
diff: @@ -1103,6 +1103,19 @@ impl RadecoModule {
  self.functions.get_mut(&offset)
  }
  + pub fn function_rename(&mut self, offset: u64, new_name: &str) -> Option<String> {
  + assert!(!new_name.is_empty());
  + let mut old_name = None;
  + if let Some(rfn) = self.function_mut(offset) {
  + old_name = Some(String::from(&*rfn.name));
  + rfn.name = From::from(String::from(new_name));
  + }
  + if let Some(ref mut src) = self.source {
  + let _ = src.raw(format!("afn {} {:x}", new_name, offset));
  + }
  + old_name
  + }
  +
  pub fn iter<'a>(&'a self) -> FunctionIter<'a> {
  FunctionIter {
  module: &self,
  