Add --human-readable option for compatibility with GNU ls

[avdv]

Description

I am using the prezto configuration for Zsh. It automatically provides useful aliases for some ls commands:

alias l='ls -1A'
alias l.='ls -d .* --color=auto'
alias ll='ls -lh'

Some Linux distributions also provide similar (more) aliases for Bash by default.

I did alias ls to colorls of course. 😄

More often than not I find myself running ll to get a long listing of a directory. Alas, since -h means "show help and exit" for colorls I only get to see the help text.

This PR adds the --human-readable option for compatibility to GNU ls and also makes -h the short option corresponding to it (exactly like GNU ls).

Since -h was used to mean "show help and exit" in colorls from the beginning, this change also keeps this effect as a special case if -h is the only argument given to colorls.

• Relevant Issues : Make colorls a drop-in replacement for ls #103
• Relevant PRs : (none)
• Type of change :
  • New feature
  • Bug fix for existing feature
  • Code quality improvement
  • Addition or Improvement of tests
  • Addition or Improvement of documentation

[codecov-io]

Codecov Report

Merging #269 into master will decrease coverage by 7.17%.
The diff coverage is 63.63%.

@@            Coverage Diff             @@
##           master     #269      +/-   ##
==========================================
- Coverage    84.9%   77.72%   -7.18%     
==========================================
  Files           7        7              
  Lines         424      431       +7     
==========================================
- Hits          360      335      -25     
- Misses         64       96      +32

Impacted Files	Coverage Δ
lib/colorls/flags.rb	78.07% <63.63%> (-5.11%)	⬇️
lib/colorls/monkeys.rb	75% <0%> (-15%)	⬇️
lib/colorls/core.rb	80.82% <0%> (-9.59%)	⬇️
lib/colorls/fileinfo.rb	75.75% <0%> (-3.04%)	⬇️

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