Add bitap_string_match algo

[edy252]

Describe your change:

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.
• Documentation change?

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Python files are placed inside an existing directory.
• All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python type hints.
• All functions have doctests that pass the automated testing.
• All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
• If this pull request resolves one or more open issues then the description above includes the issue number(s) with a closing keyword: "Fixes #ISSUE-NUMBER".

[cclauss]

This list is in alphabetical order to make it easy to spot missing values and almost impossible to add duplicates.

[cclauss]

All falsey values for pattern are equally dangerous as "".

Python and mypy are both smart enough to figure out without the type hint that if len(pattern) is assigned to m then m is an int.

Suggested change

	m: int = len(pattern)
	if m == 0:
	return 0
	if not pattern:
	return 0
	m = len(pattern)

[cclauss]

Suggested change

	state: int = ~1
	state = ~1

[edy252]

Thank you this review!

[cclauss]

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