Fix visibility issues

- Replace DYNAMIC_GRAPH_DLLEXPORT by DYNAMIC_GRAPH_DLLAPI
- Remove an unnecessary attribute
Fix some issues with the export

- No need to export template functions
- Expose some template instantiations
Move definition of template instatiation to cpp
Don't export/import template functions
[Win32] Remove template specialization declaratn, export symbols.
Merge pull request #16 from gergondet/topic/FixVisibilityIssue

Fix visibility issues