fix reason not being set after local close

[belm0]

During a local-initiated close handshake, the following incorrect behavior was observed:

• closed attribute would be None
• send_message() would be silently ignored (wsproto < 0.2.0) or leak a LocalProtocolException (wsproto >= 0.2.0)

Upon local-initiated close, closed will now have the reason, and send_message() will raise ConnectionClosed.

Fixes #158.

[coveralls]

Pull Request Test Coverage Report for Build 183

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.008%) to 95.769%

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Totals
Change from base Build 169:	0.008%
Covered Lines:	498
Relevant Lines:	520

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💛 - Coveralls