Summarize output by default (transactions available via --verbose)

I had a version of this already going in [grunt-verbosity][1], so I went ahead & moved it over here.

It will spit out something like `Created N directories, copied M files`.  Passing `--verbose` will spit out the usual output alongside the rest of the noise :)

I hope you don't mind, @geddski.

/cc @doowb, @jonschlinkert, @tkellen.

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### Before

```
 ~ ⮁ Sites ⮁ ericclemmons ⮁ grunt-contrib-copy ⮀ master ⮀ $ ⮀grunt test
Running "clean:test" (clean) task
Cleaning "tmp"...OK

Running "copy:main" (copy) task
Copying test/fixtures/test.js -> tmp/copy_test_files/test.js
Copying test/fixtures/test2.js -> tmp/copy_test_files/test2.js
Creating tmp/copy_test_mix/
Creating tmp/copy_test_mix/empty_folder
Creating tmp/copy_test_mix/folder_one
Copying test/fixtures/folder_one/one.js -> tmp/copy_test_mix/folder_one/one.js
Creating tmp/copy_test_mix/folder_two
Copying test/fixtures/folder_two/two.js -> tmp/copy_test_mix/folder_two/two.js
Copying test/fixtures/test.js -> tmp/copy_test_mix/test.js
Copying test/fixtures/test2.js -> tmp/copy_test_mix/test2.js
Copying test/fixtures/folder_one/one.js -> tmp/copy_test_v0.1.0/folder_one/one.js

Running "copy:flatten" (copy) task
Copying test/fixtures/folder_one/one.js -> tmp/copy_test_flatten/one.js
Copying test/fixtures/folder_two/two.js -> tmp/copy_test_flatten/two.js
Copying test/fixtures/test.js -> tmp/copy_test_flatten/test.js
Copying test/fixtures/test2.js -> tmp/copy_test_flatten/test2.js

Running "copy:single" (copy) task
Copying test/fixtures/test.js -> tmp/single.js

Running "nodeunit:tests" (nodeunit) task
Testing copy_test.js...OK
>> 5 assertions passed (5ms)

Done, without errors.
```

Yuck!

### After

```
 ~ ⮁ Sites ⮁ ericclemmons ⮁ grunt-contrib-copy ⮀ 57-summary ⮀ $ ⮀grunt test
Running "clean:test" (clean) task
Cleaning "tmp"...OK

Running "copy:main" (copy) task
Created 4 directories, copied 7 files

Running "copy:flatten" (copy) task
Copied 4 files

Running "copy:single" (copy) task
Copied 1 files

Running "copy:verbose" (copy) task
Created 4 directories, copied 4 files

Running "nodeunit:tests" (nodeunit) task
Testing copy_test.js...OK
>> 5 assertions passed (4ms)

Done, without errors.
```

Yum!

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Refs #44 & #57

[1]: https://github.com/ericclemmons/grunt-verbosity