IEV data structures: "Deprecated" TERMATTRIBUTE

Some terms have "deprecated" in their TERMATTRIBUTE column. What is this and how to handle it? Is it any related to entry status (#115), perhaps? This attribute is typically present next to most or all translations of given concept.

An incomplete list of such terms:

```
IEVREF LANGUAGE TERM TERMATTRIBUTE
---------- ---------- ------------------- -------------
415-03-11 en survival wind speed (deprecated)
421-01-07 en core-type transform (deprecated)
421-01-08 en core-type reactor (deprecated)
421-01-09 en shell-type transfor (deprecated)
421-01-10 en shell-type reactor (deprecated)
705-05-34 en space wave (deprecated)
881-02-62 en cathode rays (deprecated)
881-03-24 en penetrability (deprecated)
881-04-01 en ångström (deprecated)
881-04-02 en X-unit (deprecated)
881-04-04 en barn (deprecated)
881-04-09 en electrostatic unit (deprecated)
881-04-24 en first collision dos (deprecated)
881-04-52 en Roentgen-per-hour a (deprecated)
881-04-54 en exposure rate const (deprecated)
881-04-55 en specific gamma ray (deprecated)
881-12-12 en dose (deprecated)
881-12-39 en ion-yield (of radia (deprecated)
881-13-26 en counter (deprecated)
```

Some examples in Electropedia:

- http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=881-04-02
- http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=705-05-34

Related to #33.

cc @ronaldtse