add MAX_NUMBER_FILES or can be passed by a variable

[ryankert01]

in the [code] (

gdown/gdown/download_folder.py

Line 19 in a90abdf

MAX_NUMBER_FILES = 50

),
MAX_NUMBER_FILES is limited to 50, while there may be needs for downloading large folders, describe at this stackoverflow

[ryankert01]

dup with #185