Fixed AsyncGenerator build problem

On Linux/mono
Bitstring, "char" type, parameter fixes.
* BitString are now correctly returned from backend, and is correctly handled in parameters.
* BIT(1) maps to the .NET bool type and other BIT maps to BitString.
* Output parameters now work correctly for prepared queries.
* DbType.Time is now mapped to interval.
* The "char" type now returns a Char instead of a String.
* Type OIDs are sent in the Parse message.
* Optimizations when all format codes are the same in Bind message.
* Automatically infer parameter value types when setting a value.
* New NpgsqlDbType.Unknown that specifies that Npgsql should not try infer the value type, nor cast the value when written to sql, but simply write a literal string in text form.
Catch a rare error before PostgreSQL when suppressing binary backend.
Fix prepared dispose after connection close

NpgsqlCommand now listens to its connection's open/close events.
On close, sets its prepare status to NotPrepared, avoiding the
DEALLOCATE on Dispose().

A bit of additional cleanup around command/connection relations,
but further work is needed for cases where the same command gets
transferred across connections.

Fixes #393
Relates to #299
Merge pull request #394 from roji/bug393

Fix prepared dispose after connection close
Fix inappropriate messages.
Merge pull request #398 from ChenHuajun/ArgumentNullException

Fix inappropriate messages.
CRLF->LF
Disable async notification support

Which is currently incompatible with async reader
execution.

Relates to #270
Relates to #386
Merge pull request #390 from Emill/bitstring-and-parameter-fixes

Bitstring, "char" type, parameter fixes.
Bitstring, "char" type, parameter fixes.
* BitString are now correctly returned from backend, and is correctly handled in parameters.
* BIT(1) maps to the .NET bool type and other BIT maps to BitString.
* Output parameters now work correctly for prepared queries.
* DbType.Time is now mapped to interval.
* The "char" type now returns a Char instead of a String.
* Type OIDs are sent in the Parse message.
* Optimizations when all format codes are the same in Bind message.
* Automatically infer parameter value types when setting a value.
* New NpgsqlDbType.Unknown that specifies that Npgsql should not try infer the value type, nor cast the value when written to sql, but simply write a literal string in text form.
Catch a rare error before PostgreSQL when suppressing binary backend.
Unit tests around command behavior across connections

Relates to #395
Command unsubscribe from Connection state event

Fixes #395
Simplified command timeout handling
Merge branch '395'
Add RETURNING clause to Entity Framework update queries.
Merge branch 'bitstring-and-parameter-fixes'