Add a "require YAML" pragma to YAML::Dumper.

There is only one place it YAML::Dumper needs YAML.pm directly, so
expecting end users to require/use YAML themselves for this one place
consitutes a breakage of logical encapsulation for end users.

This should resolve rt#19838. Tests appear good.

YAML::Dumper's SYNOPSIS should now work as expected.
Add a test for the basic usecase of YAML::Dumper

This basically implements the minimal usecase of YAML::Dumper
in direct invocation.

If YAML::Dumper fails, so will this test, and it will output the
exception via `diag`
Update Changes. Note: This document appears not to parse with YAML anyway.
Merge pull request #11 from kentfredric/rt19838

Add a "require YAML" statement to YAML::Dumper.