README updates for new version.

Author: DanielGoldfarb

README.md

@@ -536,6 +536,7 @@ For more examples of using mplfinance, please see the jupyter notebooks in the *
 
 | Version  |  Description   | Release Date |
 |----------|--------------|----------------|
+| 0.12.3a0   | - kwarg `block=False` for non-blocking call to `mpf.plot()`<br> - customize aspect ratio, title, y-labels<br> - customize colors and other `style` aspects of plot<br> - `no_xgaps` now default to True: use `show_nontrading=True` to set no_xgaps to false<br> - secondary y-axis available to `make_addplot()`<br> - bug fix for volume widths | 2020-02-11 |
 | 0.12.0a3   | Increase mav limit from 3 to 7 different mavs  | 2020-01-16 |
 | 0.12.0a2   | Ability to save plot to a file (pdf, svg, png, jpg, ...) | 2020-01-14 |
 | 0.12.0a1   | Ability to plot arbitrary user data (in addition to basic OHLCV data).<br> - both line and scatter plots available.<br> - optionally plot on either the "main" or "lower" (aka "volume") axis. | 2020-01-09 |