Ring ideals

[dan323]

I am adding some results on rings:

• [x] Ring ideal definition
• [x] Product and sum of ideals
• [x] Prime ideal definition
• [x] Maximal ideal definition
• [x] Spectrum and Zariski topology
• [x] Ring homomorphism
• [x] Quotient of ring by ideal
• [ ] Integral domain definition
• [ ] PID definition
• [ ] Euclidean ring definition
• [ ] Ideal maximal in commutative ring iff quotient field
• [x] Ideal prime in commutative ring iff quotient integral domain
• [ ] Ring of polynomials
• [x] Ring modules

[dan323]

First part on MR #23