Add build() method that has required fields. (prometheus#187)

Author: checketts

simpleclient/src/main/java/io/prometheus/client/Counter.java

@@ -77,6 +77,16 @@ public Counter create() {
     }
   }
 
+  /**
+   *  Return a Builder to allow configuration of a new Counter. Ensures required fields are provided.
+   *
+   *  @param name The name of the metric
+   *  @param help The help string of the metric
+   */
+  public static Builder build(String name, String help) {
+    return new Builder().name(name).help(help);
+  }
+
   /**
    *  Return a Builder to allow configuration of a new Counter.
    */

simpleclient/src/main/java/io/prometheus/client/Gauge.java

@@ -75,6 +75,16 @@ public Gauge create() {
     }
   }
 
+  /**
+   *  Return a Builder to allow configuration of a new Gauge. Ensures required fields are provided.
+   *
+   *  @param name The name of the metric
+   *  @param help The help string of the metric
+   */
+  public static Builder build(String name, String help) {
+    return new Builder().name(name).help(help);
+  }
+
   /**
    *  Return a Builder to allow configuration of a new Gauge.
    */

simpleclient/src/main/java/io/prometheus/client/Histogram.java

@@ -130,6 +130,16 @@ public Builder exponentialBuckets(double start, double factor, int count) {
 
   }
 
+  /**
+   *  Return a Builder to allow configuration of a new Histogram. Ensures required fields are provided.
+   *
+   *  @param name The name of the metric
+   *  @param help The help string of the metric
+   */
+  public static Builder build(String name, String help) {
+    return new Builder().name(name).help(help);
+  }
+
   /**
    *  Return a Builder to allow configuration of a new Histogram.
    */

simpleclient/src/main/java/io/prometheus/client/Summary.java

@@ -137,6 +137,16 @@ public Summary create() {
     }
   }
 
+  /**
+   *  Return a Builder to allow configuration of a new Summary. Ensures required fields are provided.
+   *
+   *  @param name The name of the metric
+   *  @param help The help string of the metric
+   */
+  public static Builder build(String name, String help) {
+    return new Builder().name(name).help(help);
+  }
+
   /**
    *  Return a Builder to allow configuration of a new Summary.
    */