modeline-parse: parse `set` and `:` correctly
modeline-parse: parse `set` and `:` correctly

When `set` or `se` is found at the start of the modeline, it should stop parsing options after `:`.

When `modeline-parse` is called in the following file, it should _not_ recognize `tabstop=4` and `invalid_option=3`.
```
# kak: set indentwidth=0 tabstop=16: tabstop=4 invalid_option=3
```

More info: http://vimdoc.sourceforge.net/htmldoc/options.html#modeline
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