Added i) directory support, ii) FP rate args, iii) No-Save option

[revbucket]

Several changes to main.rs:

1. Added progress bar printouts vs printouts at each filename (tried to use similar formatting as in wimbd)
2. Added directory support for inputs (can pass dir as input now, only selects .json*.gz files). Same as wimbd
3. Added option to not save bloom filter at the end (but update during)
4. Added option to compute filter size dynamically given a desired false-positive rate