add coverity scan badge image
WIP: oauth1
WIP
WIP
it looks like I arrived at a first usable cut on `oauth1` now
unittest impl file split into several files
moved 3rd-party libs `base64` and `HMAC_SHA1` into the `3rdParty` sub-folder
improve/fix `create_nonce()` impl by using a `mersenne twister` implementation and protecting it with a `mutex`
fix includes
added `OAuth1` code sample to `README.md`
Merge pull request #12 from Kosta-Github/oauth1

add `OAuth1` signing support
add `doxygen` config file