Move old unit tests for Block
CMake: allow custom cxx flags using -DCMAKE_CXX_FLAGS_INIT
Add assignment operator for nullptr_t to nix::Block
Close and isOpen method for FileHDF5
Close and isOpen method for nix::File and IFile
Use the new close method in TestFile
Start unit test for Block
Fix small bugs in Block

	in  dataArrayCount
	and createSimpleTag
Test for nix::Block almost complete
Add missing operator<< to nix::DataTag
Test for nix::Block complete

Fix small bug in nix::Block::dataTagCount()
Merge pull request #46 from stoewer/master

Unit test for nix::Block (part of issue #25)

Tested locally.