Prep for 1.6 Release

[cconlon]

This PR preps for the 1.6 release, and includes the following changes:

• Moves ChangeLog from README.md to ChangeLog.md, updates with 1.6 notes
• Bumps library version to 1.6 in build.xml, pom.xml, and WolfCryptProvider.java
• Updates Windows Visual Studio project file
• Fixes native JNI feature detection for HMAC-SHA224
• Adds native feature check for PBKDF2 in WolfCryptProvider.java before broadcasting support for SecretKeyFactory
• Fixes Facebook Infer warnings about thread safety in WolfCryptSignature class
• Make RNG used in Signature class a class variable, so it is only initialized once instead of each sign() operation
• Refactor Signature threaded test to use AtomicIntegerArray
• Only runs CertPathValidator(PKIX) CRL test if native CRL has been compiled in
• Adjusts build instructions to recommend using ./configure --enable-jni for Java build consistency across JNI/JCE/JSSE
• Add synchronization to public methods of WolfCryptKeyPairGenerator
• Correctly return JNI_TRUE/JNI_FALSE from wc_ecc_verify_hash() wrapper
• Reduce extra WolfCryptRng object creations from Signature and KeyPairGenerator classes
• Call wc_RunAllCast_fips() when used with FIPS 140-3 pilot submission code