Improve exception safety and add support for swtiching error handling to exceptions

Conflicts:
	include/rapidjson/reader.h

Fixes #59 by adding bool return value for each event handler function

Also modify premake to add all projects in example folder.

This reverts commit ded7dc72.

This reverts commit fd9bc121.

GenericValue::operator= : fixup assignment operator (again)

travis-ci.org: improve config, debug GH_TOKEN issue

 * unconditionally store error state of reader after parsing
 * clear stack after parsing by using a ClearStackOnExit scope guard

In case of a user-defined RAPIDJSON_PARSE_ERROR_NORETURN that throws
an exception instead of using the Rapidjson ParseError API, the early
return paths performing the stack unwinding manually can be omitted as
well.

This patch provides a customizable RAPIDJSON_PARSE_ERROR_EARLY_RETURN
macro to remove these (then unneeded) control paths from the parsing
implementation (with and without a return value).

Secondly, clearing the parse stack is moved to a small helper struct
that calls stack_.Clear() from its destructor.  This avoids the need
for the 'goto' in the ParseStream function and ensures proper cleanup
even if e.g. a user-defined Allocator throws an exception.

In order to enable the customization of the error macros
 - RAPIDJSON_PARSE_ERROR_NORETURN
 - RAPIDJSON_PARSE_ERROR_EARLY_RETURN
the user may need to have access to the ParseErrorCode enum
already.  This requires a separate header location than the
GenericReader.

While MSVC doesn't like the explicit `.template operator=<...>` syntax
(see 4f40ed64), Clang 3.5 complains about the absence of it:

In file included from ../../test/perftest/rapidjsontest.cpp:6:
../../include/rapidjson/document.h:504:18: error: use 'template' keyword to treat 'operator =' as a dependent template name
                return (*this).operator=<StringRefType>(str);
                               ^
                               template

Delegate both operator=(StringRefType) and operator=(T) to operator(GenericValue&).

Fixes and cleanups for MSVC 

There's no need to enforce this flag during the build of the perftest
or the GoogleTest library, as both include third-party code.

There are two copies of `StrLen` in the RapidJSON code base
 * strfunc.h: rapidjson::internal::StrLen<Ch>
 * unittest.h: Strlen<Ch>

To hide a warning on MSVC, align both implementations to use
'unsigned/SizeType' as return type and add an explicit cast.

The `StringRefType` assignment operator overload
leads to a compiler error on MSVC 2005 and later:

..\..\include\rapidjson/document.h(504) : error C2951: template declarations are only permitted at global, namespace, or class scope

Drop the unneeded 'template' keyword here.

MSVC with enabled RAPIDJSON_SSE2/RAPIDJSON_SSE42 requires the explicit
definition of the `_BitScanForward` intrinsic.  This can be reliably
ensured by including "intrin.h" and properly marking '_BitScanForward'
as intrinsic.

Confirmed on MSVC 2005, 2008.
Should fix https://code.google.com/p/rapidjson/issues/detail?id=96

travis-doxygen.sh: avoid leaking the GitHub token in build log