support: specify label

[YusukeHosonuma]

Support specify label that useful for many output in source code :)

let array = ["Hello", "World"]

Debug.print(label: "🍎array", array)
// => 🍎array: ["Hello", "World"]

Debug.prettyPrint(label: "🍊array", array)
// =>
// 🍊array:
// [
//     "Hello",
//     "World"
// ]

Debug.p("🍌array") >>> array
// => 🍌array: ["Hello", "World"]

[codecov-io]

Codecov Report

Merging #77 into master will decrease coverage by 4.12%.
The diff coverage is 40.00%.

@@            Coverage Diff             @@
##           master      #77      +/-   ##
==========================================
- Coverage   78.70%   74.58%   -4.13%     
==========================================
  Files           8        8              
  Lines         385      417      +32     
==========================================
+ Hits          303      311       +8     
- Misses         82      106      +24     

Impacted Files	Coverage Δ
Sources/API/Operator.swift	0.00% <0.00%> (ø)
Sources/API/Debug.swift	75.47% <85.71%> (+4.36%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ed2d682...d6efa2e. Read the comment docs.