check namespace when reading in mzML

[ethanbass]

I think this resolves the namespace issue mentioned in #17. Not sure if we should also call the checkNamespace function in grabMzxmlData. I only incorporated it here into grabMzmlData.

[codecov-commenter]

Codecov Report

Patch coverage: 50.00% and project coverage change: -0.13 ⚠️

Comparison is base (3ffa687) 85.31% compared to head (e5545c8) 85.19%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master      #18      +/-   ##
==========================================
- Coverage   85.31%   85.19%   -0.13%     
==========================================
  Files           5        5              
  Lines        1171     1175       +4     
==========================================
+ Hits          999     1001       +2     
- Misses        172      174       +2     

Impacted Files	Coverage Δ
R/grabMSdataCode.R	87.56% <33.33%> (-0.90%)	⬇️
R/grabMzmlFunctions.R	93.03% <100.00%> (+0.02%)	⬆️

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[wkumler]

Neat! Thanks for putting in the work. I'll do some extra tests on my own shortly and check out the mzXML implementation and merge if it all looks okay.