Helper function for extractModelParameters. Used to parse each subsection of output within a given file and given results section (e.g., stdyx section) There will be many chunks if latent classes, multiple groups, multilevel features are used.
extractParameters_1chunk(filename, thisChunk, columnNames, sectionName)
name of Mplus output file being processed
character vector of output chunk from which to extract parameter values
character vector of expected column names for output chunk
A data frame (or matrix?)