New option to define indentation

[mkls]

I had a use case where I wanted to see the output of object-inspect indented,

Current output for inspect({a: 1, b: 2}):

{ a: 1, b: 2 }

New option would make this possible: inspect({a: 1, b: 2}, {indent: ' '}):

{
  a: 1,
  b: 2
}

Added a few test cases that show other cases about how it would work.

If you guys think this would be something useful to include then I'm happy to work on it a bit more and clean it up if needed. Opened this PR is just to test the idea and get some feedback.

Fixes #27.

[ljharb]

This seems like it would need to handle a lot of edge cases if it's an open-ended "indent" string.

I'd think probably the best way to do this is allowing indent to be an integer > 0, or the string '\t', and treat that as N spaces, or "tabs".

I'm not convinced this is a feature worth adding, but it's totally fine to explore what it would look like in this PR.

[mkls]

I'm also not a 100% sure this is a needed feature, but I found myself missing it. I figured I'll put in a bit of extra effort to open up a PR after I implemented it, just to see if this is needed or not.

I'm not familiar with all the use cases of this module, so I'll gracefully accept if you think this is not something you want to include.

[jaredatron]

@mkls thank you for this! Please merge! :D

[codecov]

Codecov Report

Merging #13 into master will increase coverage by 0.30%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #13      +/-   ##
==========================================
+ Coverage   97.71%   98.02%   +0.30%     
==========================================
  Files           2        2              
  Lines         219      253      +34     
  Branches       84       98      +14     
==========================================
+ Hits          214      248      +34     
  Misses          5        5              

Impacted Files	Coverage Δ
index.js	98.01% <100.00%> (+0.30%)	⬆️

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