American amount to decimal conversion; PDF decompression function; regexp-based tokenizer. Part of #1641
Use AmericanTransaction.decimal_amount in PayPal module. Part of #1641
Use AmericanTransaction.decimal_amount, closest_date, decompress_pdf and ReTokenizer in WellsFargo module. Part of #1641
Citibank module (https://online.citibank.com). Implements #1642
pep8: Various manual fixes