Generalize and speed up the tensor! macro

[IvanUkhov]

Hello,

The pull request contains a number of minor adjustments to the tensor! macro that

• make it work with a trailing semicolon,
• make it work with a trailing comma, and
• make it count rows at compile time.

Regards, Ivan

[gustavla]

Great work. Thanks for contributing!

I definitely agree it should support trailing commas/semi-colons.