Add option to keep writable transports open.

Allow qualified protocol names.

Improve minor RPC functionality.

More specifically:

+ Request records are now named. This enhances `inspect` output.
+ Custom listener hooks can now benefit from (non) `strictError` conversions.
+ Stateless listener transport errors on the writable side are now propagated
  to the listener.

Add type inference.

This release also includes:

+ Support for anonymous types.
+ Type combinations.

Add support for logical types inside unwrapped unions.

Unwrap unions and improve RPC API.

+ Unions are now represented more naturally without a wrapping object. The
  previous wrapped union type is still available to support ambiguous (less
  common) combinations of branches.
+ Protocol emitters and listeners now expose a lower level API which supports
  exchanging custom headers, running middleware, and more. Implementing custom
  transport encodings is now also much simpler.

Other changes:

+ Types can now export their schemas with defaults and other attributes (e.g.
  logical type information).
+ The default stateful RPC implementation now uses a Netty-compatible encoder
  (which will work out of the box with the Avro's Java implementation).

Prepare next major release.

+ Deprecate `LongType.using` in favor of `LongType.__with`.

Add `type.getTypeName` function.

This will make it more convenient to access union branch names (and is
more explicit than passing an optional boolean to `getName`).

Add benchmark results.

See below.

fromBuffer      |       toBuffer        |       isValid         |       (ops/sec)
---------:      |       -------:        |       ------:         |       ---------
1,301,390       |       371,872         |       26,612,629      |       ArrayString.avsc
1,622,825       |       1,431,626       |       50,125,014      |       Bytes.avsc
229,547         |       106,580         |       325,321         |       Cake.avsc
802,453         |       367,991         |       3,106,255       |       Coupon.avsc
10,020,718      |       1,483,282       |       68,603,927      |       Double.avsc
30,148,329      |       1,340,996       |       7,764,887       |       Enum.avsc
760,230         |       367,653         |       639,028         |       HistoryItem.avsc
820,911         |       485,178         |       5,708,991       |       Human.avsc
16,097,164      |       1,585,242       |       69,673,376      |       Int.avsc
11,705,891      |       1,495,754       |       37,788,289      |       Long.avsc
80,627          |       43,822          |       144,693         |       PciEvent.avsc
7,226,766       |       869,772         |       2,451,371       |       Person.avsc
4,462,827       |       814,780         |       28,920,817      |       String.avsc
5,710,550       |       840,337         |       4,086,119       |       Union.avsc
436,030         |       244,978         |       470,321         |       User.avsc

Correctly resolve namespaced messages.

Previously, the protocol's namespace would incorrectly be taken into
account when resolving requests.