Merge pull request #13 from shazino/development

MendeleySDK v1.3.2
Migrate to AFOAuth2Client for new OAuth 2.0 authentication process
Update readme about OAuth 2.0 migration
Clean code
Update copyright notice
Clean gitmodules
Clean code
Update MDLMendeleyAPIClient with `configureSharedClientWithClientID:secret:redirectURI:`
Update readme for OAuth 2.0
Update readme regarding client credentials flow
Add refreshToken: method
Fix fetch documents parameters
Clean code
Merge pull request #16 from shazino/development

MendeleySDK v1.4
Merge master (v1.4)
Remove contacts from demo app main menu
Add custom description methods
Update fetch documents in group with versions support
Update download file method to support files from groups
Fix fetch paginated group documents fetch