Add IntervalCodec and Interval class

Support the Postgres Interval type by adding the IntervalCodec.

[resolves #345][#353]

Author: Francisco Guerrero

README.md

@@ -330,7 +330,7 @@ This reference table shows the type mapping between [PostgreSQL][p] and Java dat
 | [`hstore`][psql-hstore-ref]                     | [**`Map`**][java-map-ref]|
 | [`inet`][psql-inet-ref]                         | [**`InetAddress`**][java-inet-ref]|
 | [`integer`][psql-integer-ref]                   | [**`Integer`**][java-integer-ref], [`Boolean`][java-boolean-ref], [`Byte`][java-byte-ref], [`Short`][java-short-ref], [`Long`][java-long-ref], [`BigDecimal`][java-bigdecimal-ref], [`BigInteger`][java-biginteger-ref]|
-| [`interval`][psql-interval-ref]                 | Not yet supported.|
+| [`interval`][psql-interval-ref]                 | **`Interval`**|
 | [`json`][psql-json-ref]                         | **`Json`**, [`String`][java-string-ref]. Reading: `ByteBuf`[`byte[]`][java-primitive-ref], [`ByteBuffer`][java-ByteBuffer-ref], [`String`][java-string-ref], [`InputStream`][java-inputstream-ref]|
 | [`jsonb`][psql-json-ref]                        | **`Json`**, [`String`][java-string-ref]. Reading: `ByteBuf`[`byte[]`][java-primitive-ref], [`ByteBuffer`][java-ByteBuffer-ref], [`String`][java-string-ref], [`InputStream`][java-inputstream-ref]|
 | [`line`][psql-line-ref]                         | **`Line`**|

src/main/java/io/r2dbc/postgresql/codec/DefaultCodecs.java

@@ -73,6 +73,7 @@ public DefaultCodecs(ByteBufAllocator byteBufAllocator, boolean preferAttachedBu
             new FloatCodec(byteBufAllocator),
             new InetAddressCodec(byteBufAllocator),
             new IntegerCodec(byteBufAllocator),
+            new IntervalCodec(byteBufAllocator),
             new LocalDateCodec(byteBufAllocator),
             new LocalDateTimeCodec(byteBufAllocator),
             new LocalTimeCodec(byteBufAllocator),