filterPQPdb: Filter and PQP db file
In singjc/mstools: OpenSWATH Mass Spectrometry Data Exploration

This function can be used to filter an PQP db file given a list of unmodified sequences

filterPQPdb(
  pqp_file,
  unmodified_sequence_filte,
  modified_sequence_filter = NULL
)

`pqp_file`	A character vector of the absolute path and filename of the sqMass file. (Must be .osw format)
`modified_sequence_filter`	A character vector for extraction of specific peptide(s) with modifications
`unmodified_sequence_filter`	A character vector for extraction of specific peptide(s). I.e. c('ANSSPTTNIDHLK', 'ESTAEPDSLSR', 'NLSPTKQNGKATHPR', 'KDSNTNIVLLK', 'NKESPTKAIVR')