cli example usage

[YeungOnion]

figured text output would be quick for verifying implementations with external programs, will help with verifying the implementation of #287

• example: cli tool for sampling
• example: cli tool outputs density/mass values
• example: specify required features for random_clap
• feat: implement Mode for multinomial
• example: random_clap can pmf for multinomial

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 9 lines in your changes missing coverage. Please review.

Project coverage is 93.66%. Comparing base (993a4b5) to head (0457e05).

Files with missing lines	Patch %	Lines
src/distribution/multinomial.rs	0.00%	9 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #302 +/- ## ========================================== - Coverage 93.73% 93.66% -0.08% ========================================== Files 53 53 Lines 12010 12019 +9 ========================================== Hits 11258 11258 - Misses 752 761 +9 ```

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