Update README with variable for current project version

The version in the readme can now be updated via scripting

README.adoc

@@ -1,11 +1,10 @@
-:doctype: book
+= Java JWT: JSON Web Token for Java and Android
+:project-version: JJWT_RELEASE_VERSION
 
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-= Java JWT: JSON Web Token for Java and Android
-
 JJWT aims to be the easiest to use and understand library for creating and verifying JSON Web Tokens (JWTs) on the JVM
 and Android.
 
@@ -667,23 +666,23 @@ If you're building a (non-Android) JDK project, you will want to define the foll
 
 ==== Maven
 
-[,xml]
+[source,xml,subs="+attributes"]
 ----
 <dependency>
     <groupId>io.jsonwebtoken</groupId>
     <artifactId>jjwt-api</artifactId>
-    <version>JJWT_RELEASE_VERSION</version>
+    <version>{project-version}</version>
 </dependency>
 <dependency>
     <groupId>io.jsonwebtoken</groupId>
     <artifactId>jjwt-impl</artifactId>
-    <version>JJWT_RELEASE_VERSION</version>
+    <version>{project-version}</version>
     <scope>runtime</scope>
 </dependency>
 <dependency>
     <groupId>io.jsonwebtoken</groupId>
     <artifactId>jjwt-jackson</artifactId> <!-- or jjwt-gson if Gson is preferred -->
-    <version>JJWT_RELEASE_VERSION</version>
+    <version>{project-version}</version>
     <scope>runtime</scope>
 </dependency>
 <!-- Uncomment this next dependency if you are using:
@@ -704,12 +703,12 @@ If you're building a (non-Android) JDK project, you will want to define the foll
 
 ==== Gradle
 
-[,groovy]
+[,groovy,subs="+attributes"]
 ----
 dependencies {
-    implementation 'io.jsonwebtoken:jjwt-api:JJWT_RELEASE_VERSION'
-    runtimeOnly 'io.jsonwebtoken:jjwt-impl:JJWT_RELEASE_VERSION'
-    runtimeOnly 'io.jsonwebtoken:jjwt-jackson:JJWT_RELEASE_VERSION' // or 'io.jsonwebtoken:jjwt-gson:JJWT_RELEASE_VERSION' for gson
+    implementation 'io.jsonwebtoken:jjwt-api:{project-version}'
+    runtimeOnly 'io.jsonwebtoken:jjwt-impl:{project-version}'
+    runtimeOnly 'io.jsonwebtoken:jjwt-jackson:{project-version}' // or 'io.jsonwebtoken:jjwt-gson:{project-version}' for gson
     /*
       Uncomment this next dependency if you are using:
        - JDK 10 or earlier, and you want to use RSASSA-PSS (PS256, PS384, PS512) signature algorithms.
@@ -734,12 +733,12 @@ BouncyCastle `Provider`:
 
 Add the dependencies to your project:
 
-[,groovy]
+[,groovy,subs="+attributes"]
 ----
 dependencies {
-    api('io.jsonwebtoken:jjwt-api:JJWT_RELEASE_VERSION')
-    runtimeOnly('io.jsonwebtoken:jjwt-impl:JJWT_RELEASE_VERSION')
-    runtimeOnly('io.jsonwebtoken:jjwt-orgjson:JJWT_RELEASE_VERSION') {
+    api('io.jsonwebtoken:jjwt-api:{project-version}')
+    runtimeOnly('io.jsonwebtoken:jjwt-impl:{project-version}')
+    runtimeOnly('io.jsonwebtoken:jjwt-orgjson:{project-version}') {
         exclude(group: 'org.json', module: 'json') //provided by Android natively
     }
     /*
@@ -3144,22 +3143,22 @@ scope which is the typical JJWT default).  That is:
 
 *Maven*
 
-[,xml]
+[,xml,subs="+attributes"]
 ----
 <dependency>
     <groupId>io.jsonwebtoken</groupId>
     <artifactId>jjwt-jackson</artifactId>
-    <version>JJWT_RELEASE_VERSION</version>
+    <version>{project-version}</version>
     <scope>compile</scope> <!-- Not runtime -->
 </dependency>
 ----
 
 *Gradle or Android*
 
-[,groovy]
+[,groovy,subs="+attributes"]
 ----
 dependencies {
-    implementation 'io.jsonwebtoken:jjwt-jackson:JJWT_RELEASE_VERSION'
+    implementation 'io.jsonwebtoken:jjwt-jackson:{project-version}'
 }
 ----
 
@@ -3271,22 +3270,22 @@ scope which is the typical JJWT default).  That is:
 
 *Maven*
 
-[,xml]
+[,xml,subs="+attributes"]
 ----
 <dependency>
     <groupId>io.jsonwebtoken</groupId>
     <artifactId>jjwt-gson</artifactId>
-    <version>JJWT_RELEASE_VERSION</version>
+    <version>{project-version}</version>
     <scope>compile</scope> <!-- Not runtime -->
 </dependency>
 ----
 
 *Gradle or Android*
 
-[,groovy]
+[,groovy,subs="+attributes"]
 ----
 dependencies {
-    implementation 'io.jsonwebtoken:jjwt-gson:JJWT_RELEASE_VERSION'
+    implementation 'io.jsonwebtoken:jjwt-gson:{project-version}'
 }
 ----