Update CHANGELOG.md
1.3.0
Add some advanced usages
Add section for registering conditional processor
Correct conditional processor section
Add section about registering tasks
Update USAGE.md
Update USAGE.md
Update USAGE.md
Update CHANGELOG.md
1.3.0
Merge pull request #58 from jpettersson/pvb/docs

Add usage docs for processors/tasks
Merge remote-tracking branch 'origin' into v2.0.0