Formalizes support for '-' in command names.
Formalizes support for '-' in command names.

This officially drops support for '_' in command names, which is ugly as hell.
'_' was very rarely used so it shouldn't affect too much users.

Refactor the code to be more readable.

R=stip@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1040503003

git-svn-id: bd64dd6fa6f3f0ed0c0666d1018379882b742947@294660 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

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