huge refactoring

app/handlers/converter/process/errors.go

@@ -0,0 +1,13 @@
+package process
+
+type impossibleConversionError struct{}
+
+func (e *impossibleConversionError) Error() string {
+	return "Impossible conversion"
+}
+
+type commandTimeoutError struct{}
+
+func (e *commandTimeoutError) Error() string {
+	return "The command has reached timeout"
+}