[Csv] Made some changes to the PEP

[Dave Cole]

Here is the commit message:

Trying to bring PEP up to date with discussions on mailing list.  I hope I
have not misinterpreted the conclusions.
* dialect argument is now either a string to identify one of the internally
  defined parameter sets, otherwise it is an object which contains
  attributes which correspond to the parameter set.
* Altered set_dialect() to take dialect name and dialect object.
* Altered get_dialect() to take dialect name and return dialect object.
* Fleshed out formatting parameters, adding escapechar, lineterminator,
  quoting.

- Dave

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