Add abstract streams module:
* New basic_abstract_ostream template for generic output
* New abstract_ostream, common type alias
* basic_scoped_ostream, RAII output to abstract streams
New unit_test framework:
* Header-only!
* No external dependencies or other beast modules
* Compilation options allow for:
  - Stand-alone application to run a single test suite
  - Stand-alone application to run a set of test suites
  - Global suite of tests inline with the host application
  - Disable test suite generation completely
Convert container to suite
Add abstract_chrono_io, remove dependence on chrono_io