explain metrics with more details

[yegor256]

Let's improve the details of some metrics:

• DOER
• FOUT
• HSD, HSE, HSV
• MIDX
• NCSS
• NULLS

Currently, they are very sketchy, which makes it hard to use them.

[LaithAlebrahim]

@yegor256 Just quick question , Should I document and details the metrics in ast.py or add the details to somewhere else.Thanks

[yegor256]

@LaithAlebrahim each of these metrics print their "details" as an output, for example in this line: https://github.com/yegor256/cam/blob/master/metrics/ast.py#L456 The output is " Data vs Object Encapsulation Ratio" -- this is not enough to understand what DOER metric is about. We should print a much more detailed explanation.