Improved property test coverage and found bugs

[luisggpina]

Hi!

In an effort to improve the coverage of the property tests in this project, this PR found a few bugs:

• By ensuring a better distribution of the numbers generated in LengthOpsTest.decodeIdAnyLen, the property test is now able to find examples that violate assertions:

Caused by: java.lang.AssertionError: expected:<49193> but was:<-16343>                                                                                                                                              
        at org.junit.Assert.fail(Assert.java:88)                                                                                                                                                                    
        at org.junit.Assert.failNotEquals(Assert.java:834)                                                                                                                                                          
        at org.junit.Assert.assertEquals(Assert.java:645)                                                                                                                                                           
        at org.junit.Assert.assertEquals(Assert.java:631)                                                                                                                                                           
        at com.cldellow.manu.format.LengthOpsTest.decodeIdAnyLen(LengthOpsTest.java:78) 

• By using different implementations of encoders on test ReaderTest.testVariableSize512, the property test is able to find an assertion violation:

Caused by: junit.framework.AssertionFailedError: expected:<811930252> but was:<12>                                                                                                                                  
        at junit.framework.Assert.fail(Assert.java:57)                                                                                                                                                              
        at junit.framework.Assert.failNotEquals(Assert.java:329)                                                                                                                                                    
        at junit.framework.Assert.assertEquals(Assert.java:78)                                                                                                                                                      
        at junit.framework.Assert.assertEquals(Assert.java:234)                                                                                                                                                     
        at junit.framework.Assert.assertEquals(Assert.java:241)                                                                                                                                                     
        at junit.framework.TestCase.assertEquals(TestCase.java:409)                                                                                                                                                 
        at com.cldellow.manu.format.ReaderTest.testVariableSize(ReaderTest.java:255)                                                                                                                                
        at com.cldellow.manu.format.ReaderTest.testVariableSizes(ReaderTest.java:177)                                                                                                                               
        at com.cldellow.manu.format.ReaderTest.testVariableSize512(ReaderTest.java:188)  

• Increases the coverage on IntVectorTest.testLikeArray by ensuring the case where the array grows is included in the property