fix (readtree) correct the way we parse dependency graphs

[zlav]

readtree.go does not pop the top of the stack when parsing a dependency list which results in the initial node never being removed. This results in a slightly incorrect dependency graph.

Expected Behavior:

	├── dep:one:1.0.0
	└─┬ dep:two:2.0.0
	  ├─┬ dep:three:3.0.0
	  │ └── dep:four:4.0.0
	  └── dep:five:5.0.0

Current Behavior:

	├─┬ dep:one:1.0.0
	│ └── dep:five:5.0.0
	└─┬ dep:two:2.0.0
	  └─┬ dep:three:3.0.0
	    └── dep:four:4.0.0

This PR:

1. Fixes readtree.go.
2. Fix the other generated dependency parsers.
3. Adds supporting tests inside of maven_test.go.

[codecov]

Codecov Report

Merging #385 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #385   +/-   ##
=======================================
  Coverage   47.08%   47.08%           
=======================================
  Files          68       68           
  Lines        3158     3158           
=======================================
  Hits         1487     1487           
  Misses       1522     1522           
  Partials      149      149

Impacted Files	Coverage Δ
buildtools/maven/readtree_generated.go	92.85% <100%> (ø)	⬆️
buildtools/composer/readtree_generated.go	85.71% <100%> (ø)	⬆️

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[codecov]

Codecov Report

Merging #385 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #385   +/-   ##
=======================================
  Coverage   47.08%   47.08%           
=======================================
  Files          68       68           
  Lines        3158     3158           
=======================================
  Hits         1487     1487           
  Misses       1522     1522           
  Partials      149      149

Impacted Files	Coverage Δ
buildtools/maven/readtree_generated.go	92.85% <100%> (ø)	⬆️
buildtools/composer/readtree_generated.go	85.71% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 1d39bb8...8ca7ea1. Read the comment docs.