Sundry cosmetic fixes across the board.

- Comments are migrated from ``/* */`` to ``//`` per convention.

- ``NewDefaultHistogram`` helper.

- ``Registry.Handler`` and ``Registry.YieldExporter`` deprecation.

- Cleanup of legacy import paths.

- Updating examples to use acknowledged patterns.

- Parameterizing the random parameter namespaces for ``examples/random/main.go``, which is useful for demoing population behaviors.
Merge pull request #2 from prometheus/usability/sundry

Sundry cosmetic fixes across the board.