Support for Bootstrap 4 beta

[marten-cz]

Hi, I have a quick fix for Bootstrap 4 beta for validation styling. I still left there the old classes, because anything can change in bootstrap and for backward compatibility (Bootstrap 4 alpha).

You need to add class to FieldFeedbacks manually where you define all the rules (see example). I didn't want to add there the error class to the component.

Related to #9

[codecov-io]

Codecov Report

Merging #18 into master will not change coverage. The diff coverage is 0%.

@@           Coverage Diff           @@
##           master      #18   +/-   ##
=======================================
  Coverage   86.58%   86.58%           
=======================================
  Files          15       15           
  Lines         492      492           
  Branches       90       90           
=======================================
  Hits          426      426           
  Misses         66       66

Impacted Files	Coverage Δ
src/Bootstrap4.tsx	31.25% <0%> (ø)	:arrow_up:

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[tkrotoff]

I prefer to wait for Bootstrap 4 to fix the many issues there are with forms.

[tkrotoff]

I've published branch bootstrap4 that contains some work I did a few months back (and forgot to make it public): https://github.com/tkrotoff/react-form-with-constraints/tree/bootstrap4.

With final Bootstrap v4 it will be possible to remove most of Bootstrap4.tsx code: https://github.com/tkrotoff/react-form-with-constraints/commit/8715d45ce103b3432a41994fabf81918fdc0df95#diff-14fac5149484074d6e61e3975dc46e78

[tkrotoff]

I've released v0.8.0. Took me a lot of time because it's a full rewrite (multiple rewrites actually, to find the good recipe). A few things have changed since v0.7.0. Bootstrap support has been updated to >= 4.0.0 (the way forms are handled is very different from alpha)