add support of mixed-type array

[AllenX2018]

Issue: #357

This pr adds support of mixed-type array as the spec(v1.0.0) describes:

Values of different types may be mixed.

# Mixed-type arrays are allowed
numbers = [ 0.1, 0.2, 0.5, 1, 2, 5 ]
contributors = [
 "Foo Bar <foo@example.com>",
  { name = "Baz Qux", email = "bazqux@example.com", url = "https://example.com/bazqux" }
]

[codecov]

Codecov Report

Merging #376 into master will decrease coverage by 0.29%.
The diff coverage is 88.88%.

@@            Coverage Diff             @@
##           master     #376      +/-   ##
==========================================
- Coverage   95.54%   95.24%   -0.30%     
==========================================
  Files          10       10              
  Lines        2288     2313      +25     
==========================================
+ Hits         2186     2203      +17     
- Misses         65       70       +5     
- Partials       37       40       +3     

Impacted Files	Coverage Δ
tomltree_write.go	94.69% <87.09%> (-0.83%)	⬇️
marshal.go	96.18% <100.00%> (-0.60%)	⬇️
parser.go	90.76% <100.00%> (ø)

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[pelletier]

Thank you for taking care of this, I apologize for the delay in review. I think the PR could use a test for the new check in valueToOtherSlice as it's part of the new behavior.

[AllenX2018]

I think valueToOtherSlice's changes has been covered by TestMarshalMixedTypeArray().

if mtype.Elem().Kind() == reflect.Interface {
	return nil, fmt.Errorf("marshal can't handle []interface{}")
}

I delete these lines to support []interface type when marshaling and TestMarshalMixedTypeArray() has add a test for this type. Is there any other lines/paths/changes that need to be checked?

[pelletier]

Ha my bad, looks like I misread the diff. All good, thank you for calling this out!