Travis-CI integration

This adds .travis.yml and puts build and test status badge to README.md
Merge pull request #13 from ddemidov/master

Get rid of clang-3.3 -Wconstexpr-not-const warning
Merge pull request #14 from ddemidov/travis-ci

Travis-CI integration
Use std::numeric_limits<float>::infinity() directly

Division by zero, that was used initially, results in compilation error
in VS2010
Silence MSVC security warning C4996 in system.hpp
Get rid of type convesion warnings inside VS2010