Added constant's:
- Euler-Mascheroni constant gamma γ = 0.57721566490153286060651209008240243...
('Euler's constant', not to be confused with the constant e=2.718281...)
- golden ratio conjugate constant = 0.6180339887498948 = math.rphi
- the golden ratio constant = 1.6180339887498948 = math.phi
- Euler's number (Leonhard Euler) e = 2,71828182845904523536028747135266249... = math.e
- Archimedes' constant pi π = 3.1415926535897932 = math.pi
- constant of Mitchell Feigenbaum δ ≈ 4.66920160910299067185320382046620161...