Rename Argument.help_record to get_help_record + fix typos

[alexreg]

• Rename Argument.help_record to Argument.get_help_record, to bring the name into line with Option.get_help_record (in Click).
• Typos.
• Handle None returned by Argument.get_help_record.
• Handle case of empty sequence passed to text_rows param of HelpFormatter._get_row_sep_for.

Edited by @janluke

[janluke]

Thank you very much for the PR! I'll merge this after making some changes.

[alexreg]

@janluke Thank you, I appreciate that.

[alexreg]

@janluke Looks good. Are you going to basically cherry-pick everything in this PR except the bit you just created a new issue for (reordering of super().__init__) and possibly this (not sure)? If you prefer for me to revert the bits you don't want in this PR, I can do that.

[janluke]

@alexreg I had already reverted all changes I don't want to include but they were overwritten by your force-push. Sorry, I should have been clearer I would have made the changes. No need to change anything on your end!

I'll just keep the method renaming and typo fixes. All other things will be reverted (sorry!), i.e. the return type of Argument.get_help_record is going to be Tuple[str, str]

[alexreg]

@janluke Oops, sorry about that. And yes, no worries. You kept most of the choices. Given our discussion, I agree it makes no sense to change the type signature (just the name, like you did).

Not sure if you meant to change the formatting of imports, or whether it was just my formatter messing things up here, and it accidentally crept into the commit? This one, I mean.

from typing import (Any, Callable, Dict, Iterable, List, NamedTuple, Optional,
                     Tuple, Type, TypeVar, cast, overload)

[janluke]

@alexreg No problem, fixed in master