Lets-plot

Fixed
- “Symbol not found: _NSGenericException” error on macOS [[276](https://github.com/JetBrains/lets-plot/issues/276)].

Added
- Correlation plot.

See: [Charts](https://lets-plot.org/pages/charts.html).

- 'No Javascript' mode.

Support for notebook renderers that don't execute Javascript.

See: ['No Javascript' mode](https://lets-plot.org/pages/no_js_and_offline_mode.html#no-javascript-mode)

- In tooltip customization API:
- options: `center` and `middle` (anchor).
- option 'minWidth'.

See: [Tooltip Customization](https://lets-plot.org/pages/tooltips.html).

- 'na_text' parameter in 'geom_text'

Changed
- Tooltip customization API:
- The `anchor` option moved from `theme` to `layer`:
python
geom_xxx(tooltips=layer_tooltips().anchor(anchor_value))

where `anchor_value`:
`['top_right'|'top_center'|'top_left'|'bottom_right'|'bottom_center'|'bottom_left'|'middle_right'|'middle_center'|'middle_left']`.

See: [Tooltip Customization](https://lets-plot.org/pages/tooltips.html).

Fixed
- Tooltip should appear when the mapped data is continuous [[241](https://github.com/JetBrains/lets-plot/issues/241)]
- Tooltip 'null' displayed for undefined vals [[243](https://github.com/JetBrains/lets-plot/issues/243)]
- Y-tooltip should be aligned with a tile center [[246](https://github.com/JetBrains/lets-plot/issues/246)]
- With `facet_grid` tooltip shows data from last plot on all plots [[247](https://github.com/JetBrains/lets-plot/issues/247)]

Changed
- [**breaking change**] In functions `format(field, format)` and `line(template)` in
tooltip builder, the '$' symbol is no longer used in aesthetic reference. It was replaced by the '^' (hat) symbol
(see the udated doc: [Tooltip Customization](https://lets-plot.org/pages/tooltips.html)).
- The project upgraded to Kotlin v1.4.10 (was v1.3.72).

Fixed
- No tooltip on v-line [[229](https://github.com/JetBrains/lets-plot/issues/229)]

Added
- Facilities for customization of tooltip contents and its position (see [Tooltip Customization](https://lets-plot.org/pages/tooltips.html)).
- `attribution` and other new parameters in the `maptiles_zxy()` function.
- `label_format` parameter in the `geom_text()` function.
- `scale_x_discrete_reversed()` / `scale_y_discrete_reversed()`
- `ggsave()` function (only SVG, HTML)

Fixed
- Mercator's projection computes coordinates incorrectly (`geom_map(), coord_map()`)
- Handling of `xlim,ylim` in `coord_fixed(), coord_map()`
- Colorbars: take in account limits defined in continuous color/fill scales.
- `scale_color_hue` incorrectly interprets chroma range [[206](https://github.com/JetBrains/lets-plot/issues/206)].
- `scale_color_brewer` shouldn't fail if 'type' is not specified [[203](https://github.com/JetBrains/lets-plot/issues/203)].
- `scale_fill_discrete` should not replace the default discrete scale (Brewer) with 'HUE' scale [[172](https://github.com/JetBrains/lets-plot/issues/172)].

Changed
- Lets-plot vector map-tiles are configured by default.
- PACIFIC_BLUE color (118ED8) replaced DARK_BLUE as a default color/fill value on plots.
- Default discrete color scheme is now ColorBrewer's Set2 (was Dark2)

Deprecated
- Function `gg_image_matrix()`. The new function is: `image_matrix()` in the `lets_plot.bistro.im` module.
The new function is not any longer displaying matrix by itself but returns a GGBunch object instead.
Unlike the depricated `gg_image_matrix()` function, it is not imported by `from lets_plot import *` statement.

Usage:

from lets_plot.bistro.im import image_matrix
image_matrix()

Fixed
- map_titanic.ipynb : UnboundLocalError: local variable 'map_join' referenced before assignment [[182](https://github.com/JetBrains/lets-plot/issues/182)]
- Add the `map_join` parameter to all geoms which support `map` parameter (py) [[183](https://github.com/JetBrains/lets-plot/issues/183)]

Added
- scale_x_reverse() / scale_y_reverse()
- Mnemonics for the `resolution` parameter in the `regions.boundaries()` function.

Fixed
- Exception when using `coord_map` with `xlim` [[173](https://github.com/JetBrains/lets-plot/issues/173)]
- Clipped tooltip [[155](https://github.com/JetBrains/lets-plot/issues/155)]
- Text on axis is clipped after hiding the tick-marks in theme [[160](https://github.com/JetBrains/lets-plot/issues/160)]
- Tooltip on x axis with no title shouldn't be above the axis line [[161](https://github.com/JetBrains/lets-plot/issues/161)]
- NPE while creating scale mapper when data series contains only nulls.
- Default Geocoding server url.