Moved (VERY incomplete) primefac reimplementation

README-primefac

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+`primefac-nim` is a translation of Lucas A. Brown's [primefac project](https://github.com/lucasaugustus/primefac)
+into Nim. Why? 1. I like his work and wanted it in Nim, 2. I'm trying to learn number theory.
+
+Some functions are not verbatim translation, and will be marked as such.
+This allows me to implement my own optimisations, such as using 
+the Sieve of Atkins for prime generation rather than the Sieve of Eratosthenes.

primegen.nim

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+iterator primegen(limit: int = high(BiggestInt)): int:
+  """
+  Generates primes < limit almost lazily by a segmented sieve of Eratosthenes.
+  Examples:
+  >>> primegen().take(20)
+  [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71]
+  >>> primegen(73).toSeq()
+  [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71]
+  """
+