command line return 22 if any link bad

when using the command line invocation linkchecker-markdown or python -m linkcheckmd the return code will be 22 if any link is bad, and 0 if no bad links are detected.

fix ResourceWarning, add recursive option

non-local link scans often ended with a spurious ResourceWarning. This is a known bug in aiohttp that will be fixed by them in the future. For now, the workaround is a 250 millisecond asyncio.sleep at the program conclusion.

Added a -r recursive directory option. This is for non-local scans only, as I'd need to add logic to make local scans relative to some directory. This would be straightforward if users desire--let me know.

more functionalized, better CLI, modernize type anno, pageResource

• support Hugo PageResource
• modernize type annotation
• improve CLI
• increase functionalization of code

allow python -m usage

• allow install without sudo PEP517
• use asyncio.run instead of our old Py35+ runner
• allow run via "python -m linkcheckmd"

restore use of aiohttp, Python >= 3.7

• use aiohttp for asyncio performance -- multiple times faster than reference sequential requests
• make module more robust with python >= 3.7 techniques

add local test

add local file test. This does not use the internet but just looks for filenames. It doesn't understand site structure as that is static site generator dependent.

move to src/ __main__.py layout

v1.1.1

move to src/ __main__.py layout

remove obsolete prereq

use regular Requests instead of defunct aiohttps-requests. If anything, accuracy seems to have improved as a result as compared with tools by other authors.

use logging to print debug

• use logging.info() for verbose printing
• use f-strings

initial release

v1.0.0

use argparse choices