Slight improvements.

[devsedo]

This PR provides slight improvement/shortening to a few places.

BitcoinPublicKey.swift

• The idea is to use switch for data.first. Multiple comparings can be put in a single case.
• data.first == nil equals data.isEmpty so both these cases can be put in default since we need to return false in case of being empty and in other unhandled cases as well.

Data+Hex.swift

• The idea is to let initializers decide whether to return nil or not. Firstly we need to be able to parse UInt8 to ASCII letter. Then this ASCII letter can either be HEX digit or not.
• Joining formatted strings requires less code.

Function.swift

• String concatenation with comma-separator can be done more elegant.

[vikmeup]

@devsedo this is great! There is a few changes on this PR:
#29. @alejandro-isaza will take a look at this.

Thanks for contributing.

[devsedo]

@vikmeup I was using my own git as a remote so I didn't notice that there was a commit to master before making this PR :/

[codecov-io]

Codecov Report

Merging #39 into master will decrease coverage by 0.07%.
The diff coverage is 90%.

@@            Coverage Diff             @@
##           master      #39      +/-   ##
==========================================
- Coverage   83.76%   83.69%   -0.08%     
==========================================
  Files          56       56              
  Lines        2045     2030      -15     
==========================================
- Hits         1713     1699      -14     
+ Misses        332      331       -1

Impacted Files	Coverage Δ
Sources/Ethereum/Solidity/Function.swift	100% <100%> (ø)	⬆️
Sources/Data+Hex.swift	66.66% <100%> (-7.25%)	⬇️
Sources/Bitcoin/BitcoinPublicKey.swift	73.91% <80%> (+4.34%)	⬆️

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[alejandro-isaza]

Thanks!

[vikmeup]

@devsedo if you have some free time we always have some cool problem to work now. Feel free to ping me on telegram: @vikmeup