Xmp Core Dotnet Versions Save

• Fix double instantiation of StreamWriter in XmpSerializer (#39)
• Correctly remove packet trailer (#41)
• Various code tidying (#42)
• Give XmpCore pacakge a strong name, making XmpCore.StrongName redundant and discontinued

Adjust property ordering.

• Introduce netstandard1.0 support (as well as previous net35 support)
• Fix bug in XName/string comparison
• Incorporate fixes from Java 5.1.3 to address XXE issues
• Sort properties to match Java implementation's ordering
• Allow parsing partial byte[] segment via offset/length
• Performance tweaks
• API documentation improvements
• Use TryParse instead of catching FormatException for better perf
• Introduce C# enum in place of const fields
• Internal code consolidations
• More unit tests