Add support for logarithms

Numbr is awesome. Muchas gracias for it.

I was doing some cryptography, trying to calculate how some low probabilities compare to the number of seconds until the earth is consumed by the sun:

https://numbr.dev/#KwGgDB6RYAQBQDMCWA3AprARsgNr5AewDsBKWAT3QEMAnAZ1gFdiAXPWel2AYxK4C26RjVqsAFgCgAzADZgsACbUKjAA7palUZIBMAFljjCTBrA1blFSbLgDkxJq2HnNRk7Rtx66PsUXqbvaOzpKwgGfkALQAjCC2gOfksABUETFxYImcviQBrlrGpmFRsdLpGcmp+iAGiT5+uRZKKkVpAByyIPoQiSlRHXLAtdn+gVpUdC0lscByUOW9ka0goDBzc5l1OYzs+JzcfoIuohKSLbog0cAA7HGtYGurj92wsMiMl1ewAI5M1Iq0eAIJFIklwxHgqViH1u9yesOgzxBkiAA

(The answer is about 157 quadrillion seconds, in case you were wondering.)

But I wanted to convert that result to base-2 or base-10. Seems like there's currently no support for `log()` or `ln()` functions.

Would love to see them added! 🙌