`-std=c++11` for gcc builds too
There was an issue with Travis, but we seem to be past that now.
We were using only -std=c++0x for gcc, as you can see in the diff.
resolves#134
(was #300)
I got below warning message on x86 linux machine :
```
"jsoncpp-0.10.2-p1/include/json/config.h💯 warning: ISO C++ 1998 does not support ‘long long’"
gcc version 4.4.7 20120313 (Red Hat 4.4.7-4) (GCC)
```
In reference to
* https://github.com/open-source-parsers/jsoncpp/pull/292
**long long** is supported in c++-11; for old compilers i.e `0.y.z` branch this patch should be merged.
* http://help.appveyor.com/discussions/problems/2229-v140-not-found-on-vs2105rc
```
Done Building Project "C:\projects\jsoncpp\jsoncpp.sln" (default targets) -- FAILED.
Build FAILED.
"C:\projects\jsoncpp\jsoncpp.sln" (default target) (1) ->
"C:\projects\jsoncpp\ALL_BUILD.vcxproj.metaproj" (default target) (2) ->
"C:\projects\jsoncpp\ZERO_CHECK.vcxproj" (default target) (3) ->
(PlatformPrepareForBuild target) ->
C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\V120\Microsoft.Cpp.Platform.targets(64,5): error MSB8020: The build tools for v140 (Platform Toolset = 'v140') cannot be found. To build using the v140 build tools, please install v140 build tools. Alternatively, you may upgrade to the current Visual Studio tools by selecting the Project menu or right-click the solution, and then selecting "Upgrade Solution...". [C:\projects\jsoncpp\ZERO_CHECK.vcxproj]
```
fix appveyor 32-bit windows build
I've backed rebased under #297 because AppVeyor has been failing since there, and because that was not properly based on master anyway.
* http://help.appveyor.com/discussions/problems/2229-v140-not-found-on-vs2105rc
```
Done Building Project "C:\projects\jsoncpp\jsoncpp.sln" (default targets) -- FAILED.
Build FAILED.
"C:\projects\jsoncpp\jsoncpp.sln" (default target) (1) ->
"C:\projects\jsoncpp\ALL_BUILD.vcxproj.metaproj" (default target) (2) ->
"C:\projects\jsoncpp\ZERO_CHECK.vcxproj" (default target) (3) ->
(PlatformPrepareForBuild target) ->
C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\V120\Microsoft.Cpp.Platform.targets(64,5): error MSB8020: The build tools for v140 (Platform Toolset = 'v140') cannot be found. To build using the v140 build tools, please install v140 build tools. Alternatively, you may upgrade to the current Visual Studio tools by selecting the Project menu or right-click the solution, and then selecting "Upgrade Solution...". [C:\projects\jsoncpp\ZERO_CHECK.vcxproj]
```
When I arrived at the JsonCpp GitHub page, as an intermediate C++ developer, I could not figure out how to include JsonCpp into my project. The changes I propose to the README make this much clearer, and define a clear distinction between which instructions are for those developing and contributing to JsonCpp, and those who are just using it.
