The solution of the possibly occurred "memoryError"

[HaoyuCui]

The proc_mag was default set to 40, but the providing script did not mention that.
When trying to run the given run_wsi.bat, if our slides' mag is 20x or lower, it is likely to raise the "memoryError".
Add the --proc_mag= could solve the problem, not because the RAM is not enough.
This may solve the problem #172 mentioned.