Further cleanups and improved documentation

...stjanne/libquassel/client/io/FixedDeflaterOutputStream.kt

.../justjanne/libquassel/client/io/ReadableWrappedChannel.kt

.../justjanne/libquassel/client/io/WritableWrappedChannel.kt

.../kotlin/de/justjanne/libquassel/client/util/X509Helper.kt

.../de/justjanne/libquassel/protocol/io/ChainedByteBuffer.kt

.../justjanne/libquassel/protocol/io/useChainedByteBuffer.kt

...ustjanne/libquassel/protocol/models/DccIpDetectionMode.kt

...tjanne/libquassel/protocol/models/DccPortSelectionMode.kt

...tocol/serializers/signalproxy/HeartBeatReplySerializer.kt

...l/protocol/serializers/signalproxy/HeartBeatSerializer.kt

...el/protocol/serializers/signalproxy/InitDataSerializer.kt

...protocol/serializers/signalproxy/InitRequestSerializer.kt

...quassel/protocol/serializers/signalproxy/RpcSerializer.kt

...uassel/protocol/serializers/signalproxy/SyncSerializer.kt

.../de/justjanne/libquassel/protocol/variant/QVariantList.kt

...n/de/justjanne/libquassel/protocol/variant/QVariantMap.kt

...e/libquassel/protocol/testutil/handshakeSerializerTest.kt

...e/libquassel/protocol/testutil/primitiveSerializerTest.kt

.../justjanne/libquassel/protocol/testutil/serializerTest.kt

...libquassel/protocol/testutil/signalProxySerializerTest.kt