Extract avatar classes through heritage

build.gradle

src/main/java/re/forestier/edu/Main.java

src/main/java/re/forestier/edu/rpg/Adventurer.java

src/main/java/re/forestier/edu/rpg/Archer.java

src/main/java/re/forestier/edu/rpg/Dwarf.java

src/main/java/re/forestier/edu/rpg/player.java

src/test/java/re/forestier/edu/GlobalTest.java

src/test/java/re/forestier/edu/UnitTests.java