title: Avro Field name beginning with Numeric/Integer
body: <p>I want create a Avro schema which would have Column names as 123 or 342 etc. 
  I tried to create the schema with numeric names surrounded in "`" as below :</p>
  
  <pre><code> val dataTypeMap = Map(
                      "int"-&gt; Type.INT,
                      "long"-&gt;Type.LONG,
                      "java.lang.Double" -&gt; Type.DOUBLE,
                      "java.lang.Boolean" -&gt; Type.BOOLEAN,
                      "java.lang.String"-&gt; Type.STRING
                    )
    val schemaBuilder: SchemaBuilder.FieldAssembler[Schema] = SchemaBuilder.record("test").fields()
  
    import org.apache.avro.Schema
    import org.apache.avro.SchemaBuilder
  
    val schema: SchemaBuilder.FieldAssembler[Schema] = SchemaBuilder.record("Telemetry").fields
  
    val map = Map("`1`"-&gt; 1,"`2`"-&gt;true, "`3`"-&gt; 2l,"`4`"-&gt;3.0d, "`5`"-&gt;"hello")
    val newSchema = map.foldLeft(schema)((x,y)=&gt;{       
  </code></pre>
  
  <p>x.name(y._1).<code>type</code>(Schema.create(dataTypeMap(y._2.getClass.getCanonicalName))).noDefault()
        }).endRecord()</p>
  
  <p>but failed with below error message:</p>
  
  <pre><code>Exception in thread "main" org.apache.avro.SchemaParseException: Illegal initial character: 1
          at org.apache.avro.Schema.validateName(Schema.java:1147)
          at org.apache.avro.Schema.access$200(Schema.java:81)
          at org.apache.avro.Schema$Field.&lt;init&gt;(Schema.java:403)
          at org.apache.avro.SchemaBuilder$FieldBuilder.completeField(SchemaBuilder.java:2124)
          at org.apache.avro.SchemaBuilder$FieldBuilder.completeField(SchemaBuilder.java:2120)
          at org.apache.avro.SchemaBuilder$FieldBuilder.access$5200(SchemaBuilder.java:2034)
          at org.apache.avro.SchemaBuilder$GenericDefault.noDefault(SchemaBuilder.java:2417)
  </code></pre>
  
  <p>Please help
  Thanks in Advance</p>