Correct `PushBack()` example

Fix small typo in the docs

turn implicit integer conversions into static_casts to avoid warnings

Alternative compilation fix for Solaris

Some compilers do not export the standard C library functions
to the global namespace, in case the C++ header variants are
included (<cstdlib>, <cstring>).

RapidJSON currently uses:
 * malloc, realloc, free
 * memcpy, memmove, memset, memcpy

Add an explicit namespace qualification to avoid lookup problems.

make MemoryPoolAllocator's Malloc work after Clear if a buffer was not supplied by the user

Stack: adjust growth factor

The growth factor for the `internal::Stack` helper has not been updated
together with the growth factors used in GenericValue (#130).

Discovered in https://github.com/miloyip/dtoa-benchmark/issues/1 with
assertion fail.

fix `SAX` documentation to also mention the new `Key()` method in the `Handler` concept

add `Key()` method to the `Handler` concept

It was a copy-n-paste error for the last argument of `Key()` and `String()`...

For more details see: https://github.com/miloyip/rapidjson/issues/132

This commit tries to minimize the required code changes and forwards the `Handler::Key()` calls to `Handler::String()` wherever possible in order to not break existing code; or at least not code deriving from `BaseReaderHandler` when implementing a custom `Handler`.

Initial C++11 move support

GenericValue: accept values with different allocators for read-only access

GenericValue: reduce growth factor for array/object reallocations

short string optimization