Add -exclude-files and -exclude-funcs options

[gavv]

Implement two new options allowing to specify regexp to exclude matching files and functions from diagnostics.

Options should be added to:

• command-line
• YAML config
• README

To implement -exclude-funcs, it should be enough to match function name in skip() function.

For -exclude-files, a more complicated logic is probably required. We don't have file information in skip(), so we'll need to obtain it somehow, or probably adjust AST traversal algorithm a bit.

We should also add two new tests for each option, which check that diagnostic is NOT reported for ignored files / functions.