Add the plan to resolve #11

OCTOPUS.md

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+# Forks and merges in commit history
+
+Hercules expects the commit history to be linear.
+It follows the main (zero index) branch when it encounters a fork.
+This behavior ignores all the side branches, and we are currently
+thinking how to include them into the analysis.
+
+### Plan
+
+* Commits must sorted by time.
+* When a fork is hit, clone the pipeline. Assign the old instance to the main branch and new
+instances to the sprouts. BurndownAnalysis should share the same counters for efficiency
+and simplicity, but the files must be copied.
+* Follow each branch independently. Clone side pipelines as needed.
+* Join pipelines on merge commits. Side pipelines are killed, the main instance survives.
+This will be tricky for Burndown because we need to join the files together while preserving
+the line annotations.
+* Merge commits should have diffs which correspond to CGit diffs. So far they represent the diff
+with the previous commits in the main branch.
+* The sequence of commits must be the analysis scenario: it must inform when to fork and to merge,
+which pipeline instance to apply.
+
+### New APIs
+
+* PipelineItem
+  * `Fork()`
+  * `Merge()`
+  
+### Major changes
+
+* `Pipeline`
+  * `Commits()`
+  * `Run()`
+* `Burndown`
+* `Couples`
+* `FileDiff`