Merge pull request #71 from AdaptiveConsulting/master

Fix issue with ulong NULL_VALUE and rename DirectBuffer.Position
Handle IrCollection crash from #65
[C++ OTF]: add IrCollection::map method for accessing underlying map of templateId to Ir objects for #65
[C++]: integrate in new UINT64 literal to address #51
[Java]: SemanticType is now copied from xml to IR. Issue #72.
Added support for having a sbe.target.namespace system property override the package in the schema . Enhancement #63.
[C#] Ported 63931461c7f520deda6faa24ae6aef0c07417360 (Added support for having a sbe.target.namespace system property override the package in the schema . Enhancement #63.)