Use absolute path for the link to examples

So the example link in documentation will always point to correct place.
add RAPIDJSON_NAMESPACE + _BEGIN, _END
Doxyfile: expand RapidJSON namespace macros
*.h: move to namespace macros
namespacetest.cpp: add test for separate namespace
namespacetest: add symbol check to .travis.yml
Merge pull request #193 from pah/feature/custom-namespace

Allow customization of RapidJSON namespace
Merge pull request #178 from spacewander/patch-2

Use absolute path for the link to examples
Writer: fix documentation of stackAllocator param (closes #196)
Writer: declare constructors as explicit

Avoids implicit conversion from an `OutputStream` (or an allocator pointer)
to a `Writer` instance.
DiyFp: avoid shadowing (closes #195)
Merge pull request #198 from pah/cleanup/misc

Minor (documentation) cleanups