parser.py is designed to parse a summary report from SAPGUI, combine GLs into
categories using a user-defined mapping, and produce a summary file with totals
for each of the categories.

parser.py takes three filename arguments:
* summary: the SAPGUI summary report (exported using the "download" function)
* accounts: account/category mapping file. The first column should be the category, and the second should be the account name (specifically, as it appears in the summary report --- which has a column of "     account number - account name" type elements). Additional columns may be included, but will be ignored. This may be useful for leaving notes for yourself about why an account is in a particular category.
* output: CSV output file

parser.py will read the first two files, write CSV output into the output file, and save some notes (e.g., summary rows that don't look like they have relevant info, accounts without a category, etc.) to stdout.