Cleanup the modules and improve documentation

gradle.properties

libquassel-client/build.gradle.kts

...est/kotlin/de/justjanne/libquassel/client/EndToEndTest.kt

libquassel-messages/build.gradle.kts

libquassel-messages/gradle.properties

...de/justjanne/libquassel/messages/testutil/byteBufferOf.kt

.../de/justjanne/libquassel/messages/testutil/deserialize.kt

...e/libquassel/messages/testutil/matchers/BomMatcherChar.kt

...libquassel/messages/testutil/matchers/BomMatcherString.kt

...ibquassel/messages/testutil/matchers/ByteBufferMatcher.kt

...janne/libquassel/messages/testutil/matchers/MapMatcher.kt

.../libquassel/messages/testutil/matchers/TemporalMatcher.kt

...in/de/justjanne/libquassel/messages/testutil/serialize.kt

libquassel-messages/src/test/resources/quasseltest.crt

libquassel-messages/src/test/resources/quasseltest.key

.../justjanne/libquassel/protocol/connection/ClientHeader.kt

.../libquassel/protocol/connection/ClientHeaderSerializer.kt

...de/justjanne/libquassel/protocol/connection/CoreHeader.kt

...ne/libquassel/protocol/connection/CoreHeaderSerializer.kt

...stjanne/libquassel/protocol/connection/ProtocolFeature.kt