connection style for arrows

It would be nice to have orthogonal and other types of connection style arrows when adding annotations. Matplotlib has something like:

import matplotlib.pyplot as plt

fig, ax = plt.subplots()

ax.plot([1, 2, 3], [4, 5, 2])

# Annotate with a connection line
ax.annotate("Important Point", xy=(2, 5), xytext=(1.5, 5.5),
            arrowprops=dict(arrowstyle="->", connectionstyle="arc3,rad=0.2"))

plt.show()

This would be useful for linking bars in timeline for example. Right now if you annotate the bar chart you can only add straight arrows.

该 issue 未指定文件、测试或入口点。首先定位注释箭头的实现，并将其当前的直线箭头行为与 Matplotlib 的 connectionstyle 示例进行比较。完成标准是：注释支持正交连接样式和其他连接样式，包括时间线条之间的链接，并且对所支持的样式有测试覆盖。