This program reads Nicolet FTIR spectral files (*.spa extension) and produces
text files with the first line corresponding to the spectrum title/comment, and
the following lines according to format: wavenumber, tab, absorbance, newline.

Usage: feed *.spa files as command line arguments. Files with names *.spa.txt will
be created.

Library usage:
Define char comment[256]; size_t number_of_points; float * wavenumbers, intensities.
Pass the comment pointer itself and pointers to the other variables to the spa_parse
function. Don't forget to free() wavenumbers and intensities afterwards.