Support clang-format style lines argument

yapf is based off of clang-format and takes some of the same flags, but its `lines` flag for some reason has a slightly different format than the clang-format `lines` flag:

```
-l START-END, --lines START-END
range of lines to reformat, one-based
```

vs

```
--lines= - : - format a range of
lines (both 1-based).
Multiple ranges can be formatted by specifying
several -lines arguments.
Can't be used with -offset and -length.
Can only be used with one input file.
```

Is there a technical reason for this? Obviously it's difficult to change at this point, but it would be nice to support the clang-format syntax as well. It's pretty clear what the user wants when they write `42:47` instead of `42-47` and using the syntax supported by the older and more established tool would make sense.