ENH: read_csv dialect parameter can take a string (GH8703)
Closes #8703

I wasn't sure where to put the test, hopefully this is right.

Follow-up of #8718

Looks good. Pls add a release note in v0.15.1 bug fix section referencing the original issue. Ping when pushed and green
 @thrasibule pls add a release note
 thanks! this was gr8!
merged via https://github.com/pydata/pandas/commit/0f72d3d6e7e60a8c567bb723f6ea9ad430765845 
