Upgrade Solution and Projects to VS2010
Add build output folders to .gitignore
AnyCPU removed; not supported for P/Invoke libs

Instead, two new platforms were added: x64 and x86.
Additionally, an #if was added to (temporarily) inhibit x64 builds as
the correct x64 structures and method prototypes have not yet been
defined
Win32 time_t is 64bit; fix memleaks info structs

time_t is __int64 unless _USE_32BIT_TIME_T (which by default is not
defined in rrdtool (a good thing))
Use more platform native datatypes: DateTime instead of integers etc,
which does away with dependencies to a specific bitness of the rrdtool
lib for users of the .NET binding.
Throw exceptions instead of managing integer typed return codes.