Improve Support for ValueSet Versions

[cmoesel]

Previous to this PR, cql-exec-vsac supported looking up cached value sets by specific versions -- but it completely ignored version when downloading value sets (it always downloaded the latest). Now, if a value set version is specifically requested, it will download that specific version (if that version is not already in the cache).

The unit tests show this working, but if you want to test it IRL, here is one way you could test it:

1. First you need to build a tgz of the updated cql-exec-vsac from this branch. Do this by checking out this branch, running yarn install and then running yarn pack. This will create a file named cql-exec-vsac-v1.1.1.tgz.
2. Then clone (or pull) the Pain Management Summary.
3. Open up the following file from the Pain Management Summary codebase in your favorite editor: src/cql/r4/Factors_to_Consider_in_Managing_Chronic_Pain_FHIRv400.json
4. Add the following to the ValueSet definitions around line 60:

   {
     "name" : "C19HCC SARS coronavirus 2 Qualitative Detection Laboratory Tests",
     "id" : "2.16.840.1.113762.1.4.1032.109",
     "version": "20200417",
     "accessLevel" : "Public"
   },

5. From the Pain Management Summary project, run the following command (substituting your UMLS username and password):

   node node src/utils/updateValueSetDB.js myUMLSUsername MyUMLSPassword
   

   This is downloading the value sets using the old cql-exec-vsac that does not support downloading by version.
6. Open up the following file in your favorite editor: src/cql/valueset-db.json
7. Search for 2.16.840.1.113762.1.4.1032.109 and note that it contains an empty set of codes:

   "2.16.840.1.113762.1.4.1032.109": {
     "20200417": []
   },

8. Now upgrade cql-exec-vsac in the Pain Management Summary via a command like the following (substituting the path to the tgz you created in step 1:

   yarn upgrade cql-exec-vsac@file:path/to/cql-exec-vsac/cql-exec-vsac-v1.1.1.tgz
   

9. Repeat step 5 to update the valueset-db.json file using the new cql-exec-vsac.
10. Open the valueset-db.json file again and search for 2.16.840.1.113762.1.4.1032.109 again. If this is working, you'll see that it now contains a small number of codes:

    "2.16.840.1.113762.1.4.1032.109": {
      "20200417": [
        {
          "code": "94307-6",
          "system": "http://loinc.org",
          "version": "Provisional_2020-03-31"
        },
        {
          "code": "94308-4",
          "system": "http://loinc.org",
          "version": "Provisional_2020-03-31"
        },
        // etc.
      ]
    },

[dwwinters]

Confirming tests pass and Pain Management Summary operates as described in your instructions.

[dwwinters]

You should update the readme to make it clear to users that only the url option supports versions.

[cmoesel]

You should update the readme to make it clear to users that only the url option supports versions.

Done. See c1b5d4d.