Refactor GenericValue deep-clone constructor

[POWER][XL Compiler] support IBM PowerPC / ppc64 / ppc64le and XL compiler

Avoid POWER platform compiling error and support IBM XL C++ compiler on
Linux / AIX.

Remove empty NumberStream::~NumberStream()

Fix #781

Fix nullHandler allocation bug

Remove singletons in schema classes

use _mm_cmpistri

Now owned by SchemaDocument::typeless_, and be shared to its
Schema::typeless_

Fixed another crash bug in #728

Fix for winmindef.h defining min/max macros

Remove unncessary std::move()

Fixes #762

This reverts commit c490d880.

FIx typo in documentation

The use of the vertical bar seems to break the rendering of the table in the documentation here:
http://rapidjson.org/md_doc_schema.html

Seems like we can fix it by using html encoding for the vertical bars as described in this post:
http://stackoverflow.com/questions/17319940/how-to-escape-a-pipe-char-in-a-code-statement-in-a-markdown-table/17320389#17320389

Fix compilation with older GCC versions

Older GCC versions fail compiling RapidJSON due to a warning

include/rapidjson/reader.h:578: error: suggest a space before ';' or explicit braces around empty body in 'while' statement
: warnings being treated as errors

fix #749

Add StringBuffer::GetLength()

Fix #744

Move constructor support for Writer