Lets-plot

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.

Added
- geocoding package

Fixed
- NPE on geom_tile when data contains null-s.
- The order of values in the `limits` parameter on discrete scales is ignored.
- Livemap is not shown in GGBunch.

Added
- Plugin for IntelliJ IDEA / PyCharm is available. For more info see the plugin homepage: [Lets-Plot in SciView](https://plugins.jetbrains.com/plugin/14379-lets-plot-in-sciview).

Changed
- Plots build time reduced (up to 4X)

Added
- `geom_smooth`: automatic sampling when n>1000 and the method is LOESS.

Fixed
- 'map_join' fails when the `map` argument is a dictionary [[130](https://github.com/JetBrains/lets-plot/issues/130)]

Changed
- HTML output was modified allow better integration with PyCharm.

Removed
- The deprecated method 'load_lets_plot_js()'.