Migrate copyrights to Google.
Merge pull request #105 from cgruber/migratecopyrights

Migrate copyrights to Google.
Create an initial CONTRIBUTING.md file.
Remove CLA information, and slightly re-word the acknowledgement.
Update travis-ci link.
Fix old link.
Migrate Truth to com.google.common.truth, leaving some back-ward compatibility surfaces to give time for implementers of Subjects and SubjectFactories to migrate.
Revert the deprecation of org.truth0.Truth.{ASSERT/ASSUME} until we have more people moved over inside google.
Restore final to a private constant.
Update the javadocs to use the new static method, and to use more accurate propositions.
Merge pull request #110 from cgruber/migratetogoogle

Migrate Truth to com.google.common.truth
Add assertThat() short-cut methods on Truth, and implement a test to ensure that no TestVerb.test() methods are added without a companion Truth.assertThat() method accompanying it.
Release 0.21
Migrate to com.google.truth groupId
Restore development poms.
Merge pull request #111 from google/release

Release 0.21 (and move poms to com.google.truth:truth, etc.)
Mark codegen classes as not gwt compatible, update the gwttest to address the legacy org.truth0.Truth class, and update .gwt.xml files.
Merge pull request #114 from cgruber/fixgwtagain

Mark codegen classes as not gwt compatible
Add a further GwtIncompatible tag
Add a private constructor to prevent instantiation.