Updating changelog.

Regenerated gemspec for version 0.1.21

Regenerated gemspec for version 0.1.20

Regenerated gemspec for version 0.1.18

Regenerated gemspec for version 0.1.17

Regenerated gemspec for version 0.1.16

Regenerated gemspec for version 0.1.15

Regenerated gemspec for version 0.1.14

Regenerated gemspec for version 0.1.13

Regenerated gemspec for version 0.1.12