Major Refactor with regexes allowing wiki links w spaces and w/o extensions. Basic backlinks

Feature Updates

• allow spaces in filename #12 /ht @lukakemperle @b3u @lukesmurray
• add configurable slug character: '-' or '_' or 'NONE' #17 /ht @jli
• add a very basic Backlinks Panel #13 /tx @pomdtr @b3u @lukesmurray
• add a config option to complete wiki-links without the file-extension
• add a config option to complete wiki-links with spaces

Other Improvements

• try new wikilink regex a la \[\[^\]]+\]
• change file parsing from line/word loops to line/regex loop
• switch from mocha e2e testing to jest headless testing
• write regex tests
• remove old mocha e2e test harness into new branch since it's not working w jest
• determine if wordPattern mod is nec - this still seems to be the case. in relativePaths mode, you can type . and then trigger intellisense w the keyboard shortcut and get completions, but you don't get the completions automatically without modifying the wordPattern
• tests for something#tag and https://example.com/#tag and something[[link]]
• create adapter interface wrapping vscode.getConfiguration to enable test mocking