Improve speed by parsing XML to a JSON first

[lpatiny]

The speed is improved by a factor of around 3.

@targos

Should be compatible with previous format (buffer) in Browser and Node the preferred format is now to receive a String.

Before it was:

• @param {ArrayBuffer} data - ArrayBuffer or any Typed Array (including Node.js' Buffer from v4) with the data

And now

• @param {ArrayBuffer|string} xml - Buffer(node), ArrayBuffer, typed array or String

[codecov[bot]]

Codecov Report

Merging #7 into master will decrease coverage by 0.24%. The diff coverage is 96.25%.

@@            Coverage Diff             @@
##           master       #7      +/-   ##
==========================================
- Coverage   96.49%   96.25%   -0.25%     
==========================================
  Files           2        6       +4     
  Lines          57       80      +23     
  Branches       16       21       +5     
==========================================
+ Hits           55       77      +22     
- Misses          2        3       +1

Impacted Files	Coverage Δ
src/parseCvParam.js	100% <100%> (ø)
src/util/ensureText.js	100% <100%> (ø)
src/processSpectrumList.js	100% <100%> (ø)
src/processMetaData.js	100% <100%> (ø)
src/index.js	100% <100%> (+4.25%)	:arrow_up:
src/decodeData.js	81.25% <81.25%> (ø)
... and 1 more

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