Suggestion for misspelled component name

[hrvolapeter]

Add suggestion for misspelled component name using Levenshtein distance

Closes#1816

r? @kinnison

[kinnison]

Mostly pretty good, just a couple of requests.

I also would prefer that you don't put r? @kinnison in the commit message since that ends up in the repo long-term. By all means tag me in the PR message though.

Would you like to extend this to also support making a suggestion if the user tries to add/remove a target which is misspelled?

[bors]

☔ The latest upstream changes (presumably #1833) made this pull request unmergeable. Please resolve the merge conflicts.

[kinnison]

The changes in this PR were subsumed into #1824 and merged. Thank you for your contribution to Rustup.