Java 17 compatibility (#37)

README.md

@@ -1,7 +1,7 @@
 # jox
 
 Fast and Scalable Channels in Java. Designed to be used with Java 21+ and virtual threads,
-see [Project Loom](https://openjdk.org/projects/loom/).
+see [Project Loom](https://openjdk.org/projects/loom/) (although the `core` module can be used with Java 17+).
 
 Inspired by the "Fast and Scalable Channels in Kotlin Coroutines" [paper](https://arxiv.org/abs/2211.04986), and
 the [Kotlin implementation](https://github.com/Kotlin/kotlinx.coroutines/blob/master/kotlinx-coroutines-core/common/src/channels/BufferedChannel.kt).

core/pom.xml

@@ -13,6 +13,14 @@
     <version>0.0.5</version>
     <packaging>jar</packaging>
 
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <maven.compiler.source>17</maven.compiler.source>
+        <maven.compiler.target>17</maven.compiler.target>
+        <maven.compiler.testSource>21</maven.compiler.testSource>
+        <maven.compiler.testTarget>21</maven.compiler.testTarget>
+    </properties>
+
     <dependencies>
         <dependency>
             <groupId>org.junit.jupiter</groupId>