Handle boolean values

[br0wn]

At the moment boolean values are transformed to string (ex: false becomes "false").

This PR handles boolean values as special case and does not set any value if boolean value is false which is how HTML form handles checkboxes.

[codecov]

Codecov Report

Merging #1 into master will decrease coverage by 2.95%.
The diff coverage is 50%.

@@           Coverage Diff           @@
##           master    #1      +/-   ##
=======================================
- Coverage   86.95%   84%   -2.96%     
=======================================
  Files           2     2              
  Lines          23    25       +2     
=======================================
+ Hits           20    21       +1     
- Misses          3     4       +1

Impacted Files	Coverage Δ
serialize.js	95% <50%> (-5%)	⬇️

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[octet-stream]

Hi! Thanks for your PR first.

The different serializers makes boolean transformations differently. So, I don't think it is really necessary thing, because you can always write a converter on the server that will handle boolean values. Do you?

[br0wn]

From https://www.w3.org/TR/html401/interact/forms.html#checkbox

Checkboxes (and radio buttons) are on/off switches that may be toggled by the user. A switch is "on" when the control element's checked attribute is set. When a form is submitted, only "on" checkbox controls can become successful.

A successful control is "valid" for submission.

From https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/checkbox

Note: If a checkbox is unchecked when its form is submitted, there is no value submitted to the server to represent its unchecked state (e.g. value=unchecked); the value is not submitted to the server at all.

I would argue that following standard HTML form submitting procedure would provide most suitable developer experience. Since boolean value most appropriately translates to a checkbox control, transforming it to FormData value should follow same procedure as native HTML forms do.

[octet-stream]

I understood your point. Following standards wasn't a general purpose for me, when I have made this library. It's just a tiny object/collection serializer which is more like JSON.stringify, but for transforming them to form-data and work together with then-busboy, which is transforms booleans to their original type by defalut.

Anyway, I can make this case configurable by adding strict mode, if you need it. Are you argree with that?

Also, please be consider to send pull requests from different branches, not from master (something like br0wn/patch-1). I thought it was common GitHub recommendation. Maybe I need to add contributing guidelines even for this little library.

[octet-stream]

I've implemented your proposal as serialization option. See API section in documentation for more information.

[br0wn]

@octet-stream Thank you very much :)
I apologize for the incorrect PR, I neglected to check the guidelines for proper PR flow.
Will do it properly next time. Cheers!