Add option to include/exclude binary files

[jpmv27]

This is how I implemented #48, not quite as you suggested, but with a Boolean parameter that indicates whether the tool includes or excludes binary files by default.
Please take a look and I will rework as required.
Once the code is done to your satisfaction, I'll update the docs.

[dkprice]

Looks good to me. Thanks for implementing! The only piece that will need to be added is to have an dictionary entry for turning binary off. 'sift', for example, has --binary-skip. sift is experimental at this point though so I don't see any reason to have that hold this up.

[jpmv27]

Thanks. But I'm not sure I understand your comment about sift.

Wouldn't the configuration for sift be similar to that for grep?

'opt_str_binary_switch': '--binary-skip'
'opt_bool_binary_excluded_by_default': '0'

Perhaps I misunderstand something
MV

[jpmv27]

Also, do you want a separate PR for adding the new option to the docs, or just update this one?

[dkprice]

My mistake, you're correct. This works nicely. A separate PR for the docs would be good.