implement Merge

Author: xhd2015

.gitignore

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+.DS_Store

README.md

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+# Introduction
+This library handles go-coverage files.
+It provides semantic coverage profile merging function.
+Check [merge/merge.go](merge/merge.go) for more details.
+
+Example:
+```bash
+go test -run TestMergeProfile -v ./merge
+```
+
+Old Coverage:
+![old](./img/go-coverage-old.jpg)
+
+New Coverage:
+![new](./img/go-coverage-new.jpg)
+
+Merged Coverage:
+![merged](./img/go-coverage-merged.jpg)
+
+# Algorithm
+The algorithm implementation is at [merge/merge.go](merge/merge.go).
+
+First, traverse the old and new AST tree to get each basic block's [cleaned code](./code/clean.go). Simply put, cleaned code is code that gets compiled into assembly, excluding any space and comments.
+
+Then, use [myers diff](./diff/myers/diff.go) to find unchanged blocks, see [ComputeBlockMapping](./diff/myers/map.go).In this step we map all blocks in new AST to their unchanged counterpart in old AST.
+
+Finally, use the new-to-old mapping to merge counters, for unchanged blocks, counters are added together.
+
+The algorithm effectively provides incrimental testing coverage across muiltpe changes(e.g. multiple git commits).