Initial checkable item support

[jtreminio]

edit: Ready for merging.

Related to #185

[codecov-io]

Codecov Report

Merging #186 into master will decrease coverage by 0.09%.
The diff coverage is 91.17%.

@@             Coverage Diff             @@
##             master     #186     +/-   ##
===========================================
- Coverage     93.29%   93.19%   -0.1%     
- Complexity      460      486     +26     
===========================================
  Files            26       27      +1     
  Lines          1402     1470     +68     
===========================================
+ Hits           1308     1370     +62     
- Misses           94      100      +6

Impacted Files	Coverage Δ	Complexity Δ
src/Builder/CliMenuBuilder.php	83.67% <100%> (+0.78%)	65 <3> (+3)	⬆️
src/MenuStyle.php	97.14% <100%> (+0.15%)	74 <4> (+4)	⬆️
src/MenuItem/CheckableItem.php	86.66% <86.66%> (ø)	19 <19> (?)

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[AydinHassan]

I think we should drop item extra support from this item, I can't imagine it being very useful in this circumstance. What do you think?

Overall it looks great. I've left a few other comments to address, mostly regarding renaming a few things. But I'd say go ahead and add tests :)

/cc @mikeymike

[jtreminio]

I think we should drop item extra support from this item, I can't imagine it being very useful in this circumstance. What do you think?

Overall it looks great. I've left a few other comments to address, mostly regarding renaming a few things. But I'd say go ahead and add tests :)

/cc @mikeymike

Would prefer this be a separate PR.

[jtreminio]

Pending unit tests.

[AydinHassan]

Everything looks great now apart from one comment.

[AydinHassan]

LGTM! Thanks a lot @jtreminio