Add benchmark implementations for the cnn ms example

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 60.74%. Comparing base (d6f52ff) to head (2c2fbc6).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev-postgresql #1162 +/- ## =============================================== Coverage 60.74% 60.74% =============================================== Files 85 85 Lines 4524 4524 =============================================== Hits 2748 2748 Misses 1776 1776 ``` | [Flag](https://app.codecov.io/gh/apache/singa/pull/1162/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=apache) | Coverage Δ | | |---|---|---| | [singa-cpp](https://app.codecov.io/gh/apache/singa/pull/1162/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=apache) | `60.74% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=apache#carryforward-flags-in-the-pull-request-comment) to find out more.

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