Clearly separated notion of entries and chunks, averageKeySize()/ValueSize() instead of keySize()/valueSize(), minor fixes and refactorings

src/test/java/net/openhft/chronicle/map/Issue42Test.java

@@ -34,8 +34,8 @@ public class Issue42Test {
 
         try (final ChronicleMap<CharSequence, CharSequence> map = ChronicleMapBuilder
                 .of(CharSequence.class, CharSequence.class)
-                .entrySize(18)
-                .entries(1500000)
+                .averageKeySize(5.9).averageValueSize(5.9)
+                .entries(1000000)
                 .minSegments(128).create()) {
             for (int i = 0; i < 1000000; ++i) {
                 String s = String.valueOf(i);