Update docs to correct the meter metric name in example

The meter examples defined a metric called `:bump`, however the
`bump_dat` method tries to use a metric named `bump_meter`. This raises
since this is the incorrect name of the metric. Updated the `:bump`
metric to be `:bump_meter`.
Merge pull request #2 from kb/correct-meter-example

Update docs to correct the meter metric name in example
Ignore rbenv files and remove rbenv files from source control
Update define_meter to take optional TimeUnit argument

Expose the ability for consumers to change the rate at which meters
are measured by metrics. This change maintain the original default of
TimeUnit::SECONDS and is the default value on the method signature.
Merge pull request #3 from kb/ignore-rbenv

Ignore rbenv files and remove rbenv files from source control
Merge pull request #4 from kb/meter-time-unit

Update define_meter to take optional TimeUnit argument
Default sending metrics to graphite to 60 seconds.
Bump version to 0.0.12.
Doc updates
Add link to YARD docs.
Refactor timer metric for name and time unit customization

Update the timer metric to align with how meter metrics are recorded. This
allows for more consistent metric groupings when providing a customized
metric name. In addition, allow for the default time unit to be modified by
the caller.