Variable length arithmetic

[JasperTey]

Changed

• Arithmetic expressions Add, Subtract, Multiply, Divide and Modulo now accept variable number of additional arguments beyond the first two

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This PR implements support for variable-length arithmetic arguments where applicable, as discussed in #23.

I didn't end up applying this update to the bitwise operations even though it was initially deemed mathematically possible, for two reasons:

• I questioned whether it's actually practical.
• It didn't look intuitive when I saw the Xor syntax for sqlite (({$value1} | {$value2}) - ({$value1} & {$value2})); and I didn't want to go there for this PR.

I'm open to alternate naming conventions and/or testing methodology.

[tpetry]

Thanks for your PR @JasperTey. I am currently focused on my talk on Laracon EU next week. I max make some changes to your PR and merge it when coming back.

[tpetry]

Thanks for your contribution. Its now released as 1.1.0.

I've made some small improvements:

• Moved the abstract expression to Operator\Arithmetic\ArithmeticExpression
• Added support for Power so all arithmetic expression support varargs
• Simplified the tests by using just one variadic sample (its testing less cases but more easy to understand)

[JasperTey]

Thanks for your contribution. Its now released as 1.1.0.

I've made some small improvements:

• Moved the abstract expression to Operator\Arithmetic\ArithmeticExpression
• Added support for Power so all arithmetic expression support varargs
• Simplified the tests by using just one variadic sample (its testing less cases but more easy to understand)

Fantastic, thanks for refining further. I saw you add support for Power - awesome! A quick note that the Power syntax in the README should be updated since it wasn't accounted for in my initial PR.

[tpetry]

Youre right. Completely forgot updating the Readme. Fixed.