Fix C++11 support when compiling with GCC. Closes #12.

Add the '-std=c++0x' or '-std=c++11' CXX flag to GCC compiler according to its
version.
Enable C++11 flag only for GCC >= 4.7.
Reduce the strictness of T -> bool checking, define always as x != 0

This is to mirror a change in Blaze/DataShape where we are allowing
T -> bool implicit conversions, but disallowing bool -> T for T
different from bool.
Merge pull request #17 from mwiebe/bool_nooverflow

Reduce the strictness of T -> bool checking, define always as x != 0
Disable C++11 features when CUDA is enabled
Merge pull request #19 from mwiebe/cmake-gnu-compiler

Tweak C++11 flags in cmakelists.txt
Redo the Gregorian calendar logic in a simpler date_ymd struct
Start redoing the datetime code to be ticks-only
Add a date parser which accepts a wide variety of unambiguous dates
Add support to parse RFC2822 date syntax as well
Merge pull request #21 from mwiebe/date_mods

Modifications to date type reflecting Blaze design doc
Started work on preprocessor
Fixed preprocessor to work for MSVC
Implemented map for the preprocessor
Made preprocessor map work for MSVC
Cleaned up MSVC fixes
Fixes for PP list
Fixed PP elementwise for GCC
Testing different strategies for MSVC bug
Changed syntax for lists to better support MSVC