added continuous Travis-CI, building with checking with both GCC and Clang

[neonsoftware]

Hi @mhroth,

• added .travis.yml, very minimal setup. Just running build.sh
• if it's the first Travis build for your account I'm glad to help in any ways setting it up
• the .travis.yml actually creates 2 jobs, one where GCC is installed, and one whith Clang
• added the build continuous badge in README (it points to by branch's results, will need to be updated, of course )

I additionally had to add the use of numeric macros to print intX_t uintX_t on the various architectures on commit https://github.com/neonsoftware/tinyosc/commit/46537caa6783fcf286c9292aca028400aba1c2cb, as old compilers throw actually an error on the use of lld. I love that -Werror is used so I guess it was an occasion for a further improvement towards portability. Info on the these macros here here and here.

Please let me know your opinion on any aspect, and again please feel free to demand for any change or modify it.

Cheers 👍