Dict::c_handler() is const, avoid const_cast

Whyever gcc 4.6.3 on Ubuntu 12.04 LTS (travis build farm) complained about our
const_cast syntax:
 src/bindings/cpp/shortcuts.cpp:33:42: error: expected < before <: token
... we can simply avoid that evil const_cast at all.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
travis-ci: import travis yaml controller

.travis.yml is used for automatic builds on travis build farm
(https://travis-ci.org/) if the travis service hook is enabled for the
repo on github.

This inital yaml controller will run 2 different compilers (gcc, clang). The
test suite currently fails, that's why we don't abort yet.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
Merge pull request #69 from rudimeier/travis

Travis continuous integration
Fix #59. It now checks at post and if content length is zero, it just processes the request.
Update README.rst
Update README.rst
Fixed coverity and travis-ci badges.
Badges are now proper links.
Fixed coverity found bugs at main library (src/onion).
Merge branch 'master' of github.com:davidmoreno/onion
Fixed coverity found bugs at tools. There is, maybe, a remaining memory leak.
Fixed coverity found bugs at examples.
Fixed coverity found bugs at tests.
Fixed bug at updateasset that close not exisiting nor open asset.h file. Fixed return type on 06-onion test.