Add fallback and remove unneeded implementations

[martica]

This adds a fallback in the virtual machine from inplace binary operators to standard binary operators.

Many of the standard datatypes were defining the inplace operators explicitly, either as a copy of the binary operators, or an explicit fallback. Having unneeded magic methods defined will get in the way of implementing things where fallback behaviour is needed like the __radd__ and friends operations.

Refs #46

PR Checklist:

• [x] All new features have been tested
• [x] All new features have been documented
• [x] I have read the CONTRIBUTING.md file
• [x] I will abide by the code of conduct

[martica]

The remaining test failures here are preexisting.

[danyeaw]

The remaining failing tests are failing in master as well.

@martica Congrats on your first contribution! :tada: