feat: add do_not_mutate_patterns config

[Otto-AA]

Fixes #47

This adds following config:

[tool.mutmut]
do_not_mutate_patterns = [
    # disable mutations of all logger.info/debug/... statements
    'logger\.\w+',
    # disable mutating exceptions
    'raise \w+',
]

Mutmut will:

1. check which lines of the source code match against at least one pattern
2. skip any expression that starts at any of these lines

def foo():
  logger.info( # <- line matched via pattern; all expressions starting on this line are ignored
    "Hello"
  ) # call expression ends here

  # gets mutated normally
  a = 1

It's important that we only skip expressions and not any AST node. If we would skip all AST nodes, we would also skip the "IndentedBlock" node that starts at the same line as logger.info and spans the whole function body. I think targeting expressions should cover all use cases without unexpected side effects.

This does not support multiline regexes (I did not see a use case for this, could likely be added).