Set version to v2.1.8

Add span.tensor and token.tensor attributes

Fix attrs alignment

Set version to v2.1.5

Set version to v2.1.4

Set version to v2.1.3

Set version to 2.1.2

Merge pull request explosion#3434 from Bharat123rox/narrow-unicode

Raise Error for a narrow unicode build of Python

Set version to 2.1.0

Set version to v2.1.0a13