Add Bytes parameter

[philippjfr]

Implements #408

[jbednar]

I'm glad to have a Parameter supporting bytes, but could this just be a class_ or type_ or bytes=True argument to String to enforce the the bytes type?

[MarcSkovMadsen]

Would I be able to use the Bytes parameter in Panels ReactiveHTML to efficiently transfer files or Arrow dataframes between server and client?

[philippjfr]

Would I be able to use the Bytes parameter in Panels ReactiveHTML to efficiently transfer files or Arrow dataframes between server and client?

Could look at that for sure but note that param.DataFrame parameters on ReactiveHTML are already serialized efficiently as a ColumnDataSource.

[jlstevens]

Other than Jim's docstring comment, looks good to me!

[jlstevens]

I'm glad to have a Parameter supporting bytes, but could this just be a class_ or type_ or bytes=True argument to String to enforce the the bytes type?

Given that a big part of the whole py3 transition was trying to be clear that strings and bytes are different, I think supporting bytes via a type argument to String in this way would be weird. I think a separate Bytes parameter seems like a good idea for semantic clarity.

[jbednar]

Looks good! It's a little odd for the unit test to use an IP address instead of something that would be more naturally stored as bytes, but I guess that's fine, so feel free to merge as-is.