Refactor peeling.cc and add tests associate with it

[stevenhwu]

Issue #80
Refactor peeling.cc, forward only

• add up_core() and to_parent_core() to simplify the code.
• Add a few utility functions, such as sum_over_children(), multiply_upper_lower(). Some might change after refactor reverse functions.

Add 3 boost_test

• test_sum_over_child
• test_up_core
• test_down

TODO:

• Some of these might be better in struct workspace_t
• Better check/testing for "family" can be parent-child or Dad-mom-child
• Check reverse functions
• Some debug codes might be redundant

[dng-jenkins]

Can one of the admins verify this patch?

[reedacartwright]

Jenkins, ok to test

[reedacartwright]

@stevenhwu Have you tested the performance of your changes? Eigen does the best when more operations are on the same line because it can optimize them efficiently.

[stevenhwu]

Thanks, good to know that's how Eigen works. Ran some quick (incompletely) tests, the difference is like 2s in millions of calls. Push the new test case soon.
TODO:

• Update them if these are the bottleneck
• Make it Eigen fast and without redundancy

[stevenhwu]

Update peeling.cc to ensure performance.
Based on 10 Millions calls, the difference ~ +- 2%.
TODO: better test dir layout #85

[stevenhwu]

Update peeling.cc. Some eigen related functions are defined in macro to ensure speed.
Based on 10 Millions calls or randomly generated dataset, the difference ~ +- 2%.