Add method for refreshing access tokens.
Save refresh token when requesting initial access token.
Token class separate from Infusionsoft. Refresh token improvements.
Update CHANGELOG.md.
More updates to CHANGELOG.md.
Throw ExpiredTokenException if the token expires before a request is made. Fix Authorization header.
Basic example for refreshing access tokens.
Add TokenExpiredException class.
Update README and example file.
Merge branch 'master' of https://github.com/infusionsoft/infusionsoft-php