wenjinshao

implementation of CellId.to_token and from_token slightly different from the official one

2

Specifically, the [official (?) implementation](https://github.com/micolous/s2-geometry-library/blob/master/geometry/s2cellid.cc#L168-194) strips all trailing '0's from the token generated from a CellId, and always right-pads '0's to make the input token a 16-character hex representation before...