This PR adds linting for whitespace after control code (-). With this patch, a line that doesn't have a single whitespace between - and the code gets registered as an offense:

# bad (no whitespace)
-cond

# bad (too much whitespace)
-  cond

# good (single whitespace)
- cond

By all accounts, this seems to be the preferred style in slim documentation.

In the implementation, I added this feature to the existing linter ControlStatementSpacing. I did this because linters for control code have ControlStatement in the name (e.g. EmptyControlStatement, CommentControlStatement or ConsecutiveControlStatements). Let me know if this should be moved to a new linter, although I'm not sure how I'd name it because this linter is currently used to lint output code instead of control code.