Switchboard Dialog Act Corpus added under `datasets/swda`
Pleased to announced that I added my first dataset **Switchboard Dialog Act Corpus**.


I think this is an important datasets to be added since it is the only one related to dialogue act classification. 

Hope the pull request is ok. Wasn't able to see any special formatting for the pull request form.


The Switchboard Dialog Act Corpus (SwDA) extends the Switchboard-1 Telephone Speech Corpus, Release 2,
with turn/utterance-level dialog-act tags. The tags summarize syntactic, semantic, and pragmatic information
about the associated turn. The SwDA project was undertaken at UC Boulder in the late 1990s.


[webpage](http://compprag.christopherpotts.net/swda.html)

[repo](https://github.com/NathanDuran/Switchboard-Corpus/raw/master/swda_data/)

Please contact me for any support!

All tests passed and followed all steps in the contribution guide!


Need to fix code formatting.