bump version to 0.3.0 for locstream capability

Merge branch 'master' of https://github.com/JiaweiZhuang/xESMF

Bump version number from 0.2.0 to 0.2.1

Use coarser grid in the first rectilinear tutorial

To speed-up computation and save memory.
The previous output data was near 1GB; can crash tiny cloud VMs.

bump version number for new release

Add python requirement

Fix license in setup.py

Use basic scipy.sparse.coo_matrix.dot. Faster than sparse.tensordot.