jrep: support equivalent of grep options '--exclude', '--exclude-from', '--exclude-dir, and '--include'

[arames]

Options should be compatible with grep.

In many situations the user may not want to specify excluded targets manually on the command line, so also consider:

• Introducing 'rc' configuration files for the options. Maybe introduce an option disabling the rc files.
• Using an environment variable to store predefined options.
• Introducing an option to automatically exclude versioning data (.git, .svn, etc.).