New linters/detectors: hard-tabs, no-eof-nl, merge-conflict-markers, new-todos

[MicahElliott]

Already have some, but could potentially combine some/all into one, since these are all similar and pretty simple.

• secrets detector: filename, aws-looking creds (probably just use https://github.com/Yelp/detect-secrets)
• hard tabs
• missing newline at eof
• merge conflict markers
• new-todos (improved git-confirm.sh)
• local-paths (hard-coded in sources)
• line endings ("\n" # or "\r\n" for Windows-style newlines)
• BOM check