Finally, fix logging format

[y8]

Sorry, I'm kinda late for 2.0 release, but still.

Before this pull request, when you copy & paste stuff from logs it was like:

mongo>  {"$query"=>{:likes=>{"$exists"=>false}}, "$explain"=>true, "$orderby"=>{:_id=>1}, "$maxScan"=>10} flags=[] limit=0 skip=0 batch_size=nil fields=nil
SyntaxError: Unexpected token >

 (ﾉಥ益ಥ）ﾉ ┻━┻

After this pull request and after Moped.log_format = Moped::LogFormat::ShellFormat it is like:

mongo> db.users.find({"likes":{"$exists":false}})._addSpecial({"$maxScan":1}).explain(true)
{
    "cursor" : "BasicCursor",
    "isMultiKey" : false,
    "n" : 1109994,
    "nscannedObjects" : 1109994,
    "nscanned" : 1109994,
    "nscannedObjectsAllPlans" : 1109994,
    "nscannedAllPlans" : 1109994,
    "scanAndOrder" : false,
    "indexOnly" : false,
    "nYields" : 8671,
    "nChunkSkips" : 0,
    "millis" : 5979,
    "allPlans" : [
        {
            "cursor" : "BasicCursor",
            "isMultiKey" : false,
            "n" : 1109994,
            "nscannedObjects" : 1109994,
            "nscanned" : 1109994,
            "scanAndOrder" : false,
            "indexOnly" : false,
            "nChunkSkips" : 0
        }
    ],
    "server" : "yopp-air:27017",
    "filterSet" : false,
    "stats" : {
        "type" : "COLLSCAN",
        "works" : 1109996,
        "yields" : 8671,
        "unyields" : 8671,
        "invalidates" : 0,
        "advanced" : 1109994,
        "needTime" : 1,
        "needFetch" : 0,
        "isEOF" : 1,
        "docsTested" : 1109994,
        "children" : [ ]
    }
}
ヽ(^。^)ノ

Give it a try rake MOPED_LOG_FORMAT=shell MOPED_PRINT_LOG=1

Few notes:

1. It's backward compatible: useless DefaultFormat is default!
2. Now in technicolor!
3. Be creative, make your own log formatter without dirty patching!
4. ShellFormat is not fully tested. It might produce something incompatible in some cases. Feedback is very welcome.

[coveralls]

Coverage decreased (-2.11%) when pulling 5ceef14 on y8:master into 2d92a6b on mongoid:master.

[coveralls]

Coverage decreased (-1.75%) when pulling 13e87d8 on y8:master into 2d92a6b on mongoid:master.