Minor improvements to Scalar class documentation and code

[KostaIlic2]

• This contribution adheres to CONTRIBUTING.md.

What does this Pull Request accomplish?

This PR resolves issues #230 and #231.

Summary of changes:

1. Improved documentation for comparison functions.
2. Improved formal argument names for comparison functions. Previous name, "value", was confusing because objects of scalar class have a data member also called "value".
3. Made all arguments for all comparison functions positional only, for consistency, and to prevent unintended reliance on formal argument names.
4. Refactored duplicated string for an exception into a private function.

Why should this Pull Request be merged?

The changes increase value of the library.

What testing has been done?

I executed prescribed static code and automated test protocols. Since there were no functional changes, I did not introduce any new automated tests.

[KostaIlic2]

Inspired by @bkeryan's statement that equality comparison operators are always supported I decided to split comparison section of the document between equality and order comparison operators. I like new organization better.

[KostaIlic2]

@bkeryan, I see we use of slightly different terminology and orthography within scalar.py. Some were there before this PR. Here is what I found with the version of the file in this PR:

• Scalar Data Type - line 3 and later
• Scalar - line 6 and later
• scalar data object - line 6 and later
• scalar data class - line 33 and later
• scalar objects - line 61 and later
• scalars - line 69 and later
• Scalar objects - line 109 and later

Would you like me to address this inconsistency as part of this PR?

[bkeryan]

@bkeryan, I see we use of slightly different terminology and orthography within scalar.py. Some were there before this PR. Here is what I found with the version of the file in this PR:

• Scalar Data Type - line 3 and later
• Scalar - line 6 and later
• scalar data object - line 6 and later
• scalar data class - line 33 and later
• scalar objects - line 61 and later
• scalars - line 69 and later
• Scalar objects - line 109 and later

Would you like me to address this inconsistency as part of this PR?

No, I think this is fine.

"object" vs. "class" is intentional. An object is an instance of the class.

"class" is a specific "data type".

"Scalar" is lowercase in prose and capitalized when referring to the class name.

"data object" vs. "object" and "data class" vs. "class" is a minor inconsistency.

[bkeryan]

Looks good to me.