Adding loader for SMC dataset

[tanmayy24]

Please include the following information at the top level docstring for the dataset's module mydataset.py:

• [x] Describe annotations included in the dataset
• [x] Indicate the size of the datasets (e.g. number files and duration, hours)
• [x] Mention the origin of the dataset (e.g. creator, institution)
• [x] Describe the type of music included in the dataset
• [x] Indicate any relevant papers related to the dataset
• [x] Include a description about how the data can be accessed and the license it uses (if applicable)

Dataset loaders checklist:

• [x] Create a script in scripts/, e.g. make_my_dataset_index.py, which generates an index file.
• [x] Run the script on the canonical version of the dataset and save the index in mirdata/indexes/ e.g. my_dataset_index.json.
• [x] Create a module in mirdata, e.g. mirdata/my_dataset.py
• [x] Create tests for your loader in tests/datasets/, e.g. test_my_dataset.py
• [x] Add your module to docs/source/mirdata.rst and docs/source/table.rst
• [x] Run black, flake8 and mypy (see Running your tests locally).
• [x] Run tests/test_full_dataset.py on your dataset.
• [x] Check that codecov coverage does not decrease.

If your dataset is not fully downloadable there are two extra steps you should follow:

• [x] Contacting the mirdata organizers by opening an issue or PR so we can discuss how to proceed with the closed dataset.
• [x] Show that the version used to create the checksum is the "canonical" one, either by getting the version from the dataset creator, or by verifying equivalence with several other copies of the dataset.
• [x] Make sure someone has run pytest -s tests/test_full_dataset.py --local --dataset my_dataset once on your dataset locally and confirmed it passes.

Please-do-not-edit flag

To reduce friction, we will make commits on top of contributor's pull requests by default unless they use the please-do-not-edit flag. If you don't want this to happen don't forget to add the flag when you start your pull request.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 97.95918% with 1 line in your changes missing coverage. Please review.

Project coverage is 97.07%. Comparing base (c1e3cf9) to head (3b1c385).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #620 +/- ## ======================================= Coverage 97.07% 97.07% ======================================= Files 63 64 +1 Lines 7341 7390 +49 ======================================= + Hits 7126 7174 +48 - Misses 215 216 +1 ```