Improves endian detection

Fix #66 by adding Writer::Reset() and Writer::IsComplete()

Since __BYTE_ORDER__ only avaliable since GCC 4.6.0, add more detection.

Fix uploading Doxygen documentation to GH pages from Travis CI

Instead of fiddling with the non-working GIT_ASKPASS/core.askpass
setup, simply store the required Git credentials directly in
~/.git-credentials, which is used by Git's "store" credential helper.

Works on https://travis-ci.org/pah/rapidjson.

Note it redefines RAPIDJSON_ASSERT() to throw exception in unittest and
check for assertion with gtest.

Avoids messing with global config when running the script
manually on a developer machine.

This reverts commit 62250923.

This reverts commit 025c516f.

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