Readme: Add instructions on specifying tracked fields

Readme: Add instructions on specifying tracked fields
Reset audited_user when yield raises exception

Because if it's not set to nil, all audits made from the sweeper will
use the user from this block instead of current_user, until
Audit.as_user is called again.
Fix lixenses.

Add missing LICENSE files and reference license in .gem metadata.
Merge pull request #121 from thomasklemm/master

Readme: Add instructions on limiting fields
Merge pull request #127 from voxik/fix-licenses

Fix lixenses.
Merge branch 'reset_audited_user_when_yield_raises_exception' of https://github.com/flugsio/audited into flugsio-reset_audited_user_when_yield_raises_exception

* 'reset_audited_user_when_yield_raises_exception' of https://github.com/flugsio/audited:
  Reset audited_user when yield raises exception
Check for a truthy value instead of explicit true value
Make sweeper code thread-safe
Merge pull request #141 from aduraj/master

Sweeper code isn't thread-safe.
Add test to ensure which attributes are not audited when uses ':only'

This scenario is very common when running rake db:migrate from scratch
in a rails app that uses devise.