add AppVeyor CI support for checked Windows builds

Move `gtest_force_shared_crt` option to Win32 VC only.

Mentioned in #240

Fix typesetting

CMake support

reader.h: warning fixes (closes #235, closes #236)

Reorganized some features. Try to make the text clearer in features and
tutorial.

Add std::string overload to Writer when RAPIDJSON_HAS_STDSTRING defined

Use aligned SSE register load intrinsic.

The code goes to the trouble of ensuring that data is aligned at a
16-byte boundary, then goes ahead and uses the unaligned form of the
load intrinsic _mm_loadu_si128.

Either the code shouldn't bother aligning the data to the start of the
whitespace, or it should use the aligned form of the intrinsic.

Correct Value(kStringType) and more assertions

Reader::Parse{Array,Object}: simplify switch

Closes #223.

Fix an issue with building a reader on Windows x64. 

Fix an issue with Windows x64. Including the rapidjson reader.h requires <intrin.h> to be included or _umul128 will be undefined.

stringbuffer.h: add missing include for std::move (fixes #208)