Signal-analog

Added

* ListCharts learned how to filter legend options via the
`with_legend_options` builder
* Future chart types that can filter legend options may now take advantage
of the `signal_analog.charts.LegendOptionsMixin` class
* The `FieldOption` class has learned to accept `SignalFxFieldOption`s which
provide mappings between field options seen in the UI and those used in the
API
* e.g. `Plot Name` in the UI and `sf_originatingMetric` in the API
* A new `TextChart` object has been added to `signal_analog.charts` that
enables text descriptions to be added to dashboards.
* `PublishLabelOptions` has learned to accept prefix, suffix, and unit
arguments when labelling data on charts.

Changed

* `PublishLabelOptions` has learned to accept all arguments as optional
with the exception of the `label` argument.

Fixed

* A fix has been added for Python 2 users that prevented successful
dashboard updates.

For assistance migrating from 1.x to 2.x please consult the
[migration guide][migration-1x].

Added

* Add support for the `dimensions`, `fill`, `integrate`, `kpss`,
`rateofchange` methods


Removed

* `map` method support has been removed
* It didn't work properly to begin with, and will require some finagling
to get right given our approach to building SignalFlow statements

Fixes

* `top` and `bottom` method signatures have been fixed to use `count`, `by`,
and `percentage` arguments
* The following functions have been updated to raise an error if both
`by` and `over` are defined in the same method call:
* `count`, `max`, `mean`, `mean_plus_stddev`, `median`, `min`,
`percentile`, `random`, `size`, `stddev`, `sum`, `variance`
* `delta` has been updated to no longer accept any method arguments
* `ewma` has been updated to support the `over` key

* Add combinators for less-than-or-equal-to (`LTE`) and greater-than-or-equal-to (`GTE`)

* Added `include_zero` method to `TimeSeriesChart` to allow setting the `includeZero` option.

* Fix detector update logic to include all fields instead of just name/description

* Implements functionality to add event overlays and selected (default) event overlays to dashboards
at dashboard creation or update. Includes wildcard matching using the asterisk (*) symbol.