Restore public constructors for compatibility (#428)

Restore public constructors for compatibility

CoreMatchers, MatcherAssert, and Matchers had private contructors added
to fix javadoc warnings. Unfortunately, this can break existig users of
the classes.

Fixes #427

Author: tumbarumba

CHANGES.md

@@ -25,7 +25,9 @@ these methods will need to be updated. The following methods are affected:
 
 ### Improvements
 
-* Javadoc improvements and cleanup ([PR #420](https://github.com/hamcrest/JavaHamcrest/pull/420))
+* Javadoc improvements and cleanup ([PR #420](https://github.com/hamcrest/JavaHamcrest/pull/420),
+[#427](https://github.com/hamcrest/JavaHamcrest/issues/427),
+[PR #428](https://github.com/hamcrest/JavaHamcrest/pull/428))
 * Derive version from git tags ([PR #419](https://github.com/hamcrest/JavaHamcrest/pull/419))
 * Migrate all tests to JUnit Jupiter ([PR #424](https://github.com/hamcrest/JavaHamcrest/pull/424))
 

hamcrest/src/main/java/org/hamcrest/CoreMatchers.java

@@ -13,7 +13,10 @@
 @SuppressWarnings("UnusedDeclaration")
 public class CoreMatchers {
 
-  private CoreMatchers() {
+  /**
+   * Unused
+   */
+  public CoreMatchers() {
   }
 
   /**

hamcrest/src/main/java/org/hamcrest/MatcherAssert.java

@@ -6,7 +6,10 @@
  */
 public class MatcherAssert {
 
-    private MatcherAssert() {
+    /**
+     * Unused.
+     */
+    public MatcherAssert() {
     }
 
     /**

hamcrest/src/main/java/org/hamcrest/Matchers.java

@@ -22,7 +22,10 @@
 @SuppressWarnings({"unused", "WeakerAccess"})
 public class Matchers {
 
-  private Matchers() {
+  /**
+   * Unused
+   */
+  public Matchers() {
   }
 
   /**