[FEATURE] PeakFileOptions extension

- extend PeakFileOptions by an maximal_data_pool_size_ parameter which
  specifies how many spectra should be read before being processed
[FEATURE] parallel spectra processing for mzML

- while reading, the spectra are decoded in parallel which allows for
  faster read times of the mzML data format
[FEATURE] parallel spectra processing for mzXML

- while reading, the spectra are decoded in parallel which allows for
  faster read times of the mzXML data format.
[FIX,TEST] fix typo, add test
[FIX] fixes suggested by Chris

- correctly handle update of shared variable
- move PeakType out of loops
[FIX] stop parsing upon error
[FIX] flush data after seeing end of XML file
[FIX] mzXML does not have chromatograms
[FIX] remove throwing destructor

- do not call populate in the destructor since this function might throw
Merge pull request #702 from hroest/feature/ParallelReader

Feature/parallel reader