Previously FileBuffer was actually buffering to file _and_ `cout`
at the same time.
This is behaviour is now split, with common functionality
in OstreamBuffer. The old behviour is kept by using
a new DualLogStream in the actual logger. This uses the
extensible CombinedBuffer that can be used as a meta container
for any SuspendableStrBuffer.

Float cmp tests for integer, fixes #15 

also add tests for std::size_t

mainly this pulls up variable definitions into the fixture ctor
it also disambiguates the used DEFAULT_EPSILON

this is an API breaking change as an additional param is added to
`ValidationInterface::msg` and the ostream inserter for validation
objects necessarily removed

this automagically handles all compares for vector types too

- bracket etc placement is not whitespace
- typos
- include guards

- run it only once across builders
- set binary name via git-config.env and install it too