Minor fixes

[kazu-yamamoto]

This PR exposes necessary types (no haddock warnings anymore), updates document and fixes coding style.

[kazu-yamamoto]

Also this fixes #228.

[ocheron]

I don't think it's a good idea to expose the internals of TLSParams.
Users don't need to provide their own instances.

[kazu-yamamoto]

The original code is exporting the name TLSParams but not its methods.

1. The original approach

• Haddock warning: getTLSCommonParams getTLSRole doHandshake doHandshakeWith
• TLSParams connects contextNew and ClientParams nicely

2. Stopping TLSParams, too

• Haddock warning: TLSParams
• No clue to connect contextNew and ClientParams

I think that 2) is not good. So, I will take the original approach.

[kazu-yamamoto]

Merged. Thank you for your review.

[ocheron]

Could you also remove CommonParams and Role, and revert the change to Network.TLS.Context ?

Weeds exported
* Network.TLS.Context
  - doHandshake
  - doHandshakeWith
  - getTLSCommonParams
  - getTLSRole

[kazu-yamamoto]

Done.