Enumerate type counts for multiple types; enable secondary reads

[predictive]

This keeps a count of how many of each type is found for a given field, to assist in making decisions about schema changes.

The user can now pass slaveOk=true to mongo when reading from a secondary replica set member.

Note: This changes the JS type of 'types' from Array to Object, which could break programs parsing the JSON output of Variety:

[
        {
                "_id" : {
                        "key" : "_id"
                },
                "value" : {
                        "types" : {
                                "ObjectId" : 119
                        }
                },
                "totalOccurrences" : 119,
                "percentContaining" : 100
        },
        {
                "_id" : {
                        "key" : "lat"
                },
                "value" : {
                        "types" : {
                                "Number" : 119
                        }
                },
                "totalOccurrences" : 119,
                "percentContaining" : 100
        },
        {
                "_id" : {
                        "key" : "lon"
                },
                "value" : {
                        "types" : {
                                "String" : 1,
                                "Number" : 118
                        }
                },
                "totalOccurrences" : 119,
                "percentContaining" : 100
        }
]

[todvora]

Hi Jeff,
Thanks for your PR. It looks like useful features to have. Let me check the source code and adapt test cases.

What do others think?

Best regards,
Tomas

[todvora]

I just created new branch and adapted the tests to this PR. See https://github.com/variety/variety/tree/objectrocket-master.

How about a merge, @JamesCropcho? Any comments?

[JamesCropcho]

Hello Jeff and Tomáš:

Jeff, thank you so much for your contribution to Variety. In addition to hopefully benefiting you, it will surely benefit the few thousand Variety users around the world.

I would have like to receive one PR for the slaveOk and one for the type enumeration, but I won't be nearly picky enough to request resubmission. (Seriously, thank you!)

Tomáš, I see your branch passes the test suite, yet we want to semantically give credit to Jeff, i.e. merge his PR so there is a paper trail (ideally). How about you merge his PR, then merge your branch into master—does that sound like a plan?

Best to You Both,
James Cropcho

[todvora]

Hi,
Merged and cherry-picked the test commits from the branch. Tests are passing on master.

Thank you!

[JamesCropcho]

Looking great, you two. Mission accomplished.