Merge pull request vnpy#2256 from vnpy/dev

v2.0.9

Merge pull request vnpy#2196 from vnpy/dev

Dev

Merge pull request vnpy#2097 from vnpy/dev

Dev

Merge pull request vnpy#1947 from vnpy/dev

Dev-2.0.6

Merge pull request vnpy#1899 from vnpy/dev

[Add] clear_button to clear log monitor

[Mod]update README.md

Merge pull request vnpy#1716 from vnpy/dev

Dev

Merge pull request vnpy#1706 from vnpy/dev

Dev

Merge pull request vnpy#1706 from vnpy/dev

Dev

Merge pull request vnpy#1615 from vnpy/DEV

Dev