Math expansion

[phcreery]

This PR is aimed at #30
It happens to have a list of other enhancements too.

• : shortcuts to :=
• Parentheses
• pi!
• Trigonometric Functions
• Numbers do not default to float
  • Needs discussion
• Evaluation Types
  • rewrite
    • 
  • expand
    • need to add \\expand to latex dictionary
  • simplify
  • factor
  • solve (for explicit variable)
    • Defaults to only variable if only 1 is used.
    • 

[stefnotch]

Could you remove the public/__pycache__/mathjson.cpython-38.pyc file? If you think that its easy to accidentally create a public/__pycache__ folder, feel free to add it to the .gitignore while you're at it.

[stefnotch]

This is looking pretty solid now! Its definitely a huge improvement over the status quo. While there are still parts that could be improved, I'd be happy to leave them for future pull requests.
What do you think?

[phcreery]

Thanks! Yea, most of these were the low hanging fruit. I'm cool with that. I will complete the review and pull this up from draft state.

[stefnotch]

Looks great!