Transbigdata

Add the Triangle and hexagon gridding methods, the methods are vectorized and fast:
- Triangle grids: `GPS_to_grids_tri` and `gridid_to_polygon_tri`
- Hexagon grids: `GPS_to_grids_hexa` and `gridid_to_polygon_hexa`

See [Example](https://transbigdata.readthedocs.io/en/latest/gallery/Example%202-Grid-base%20processing%20framework%20of%20TransBigData.html) for details.

- Modify code format to fit the standard of flake8.
- Fix bug in `getbusdata`, now it work perfectly.

fix bug in `getbusdata`

Add method `grid_params_optimize` to optimize the grid params.
Drop method `getbusdata` because it produce uncorrect data.

Add two functions for isochrone download:
- `get_isochrone_mapbox`: Obtain the isochrone from mapbox isochrone.
- `get_isochrone_amap`: Obtain the isochrone from Amap isochrone.

Grids are now support rotate with given angle:
- grid `params` are now support the fifth parameter `theta` to represent the rotation angle.
- `GPS_to_grids`,`grids_centre`,`rect_grids`,`gridid_to_polygon`,`regenerate_params` are rewrite to support grids with angle.

The method `grid_from_params` is similar with the method `rect_grids`, so its function is merged into `rect_grids`.