Custom hooks to allow issue reporting somewhere else than stdout ? #37

[voytech]

Following changes has been made:

• Modified core.clj file:
  • added additional parameter "details" for each linting function (this is atom vector to aggregate issues)
  • added some helper functions supporting issue aggregation.
• Added section to README.md which shows returned result record format.

If You think there are some things that should be or may be done better - just let me know. I am waiting on any suggestions and recommendations.