Initial project import

tools/v/vlib/math/fractions/README.md

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+# math.fractions
+
+`math.fractions` provides exact rational arithmetic.
+
+## Existing `i64` API
+
+```v
+import math.fractions
+
+f := fractions.fraction(4, 8)
+assert f.reduce().str() == '1/2'
+```
+
+## Generic backends
+
+`fractions.Rational[T]` supports signed builtin integers and `math.big.Integer`.
+
+```v
+import math.big
+import math.fractions
+
+huge := big.integer_from_string('1000000000000000000000000000000')!
+f := fractions.big_fraction(huge, big.integer_from_int(3))
+g := fractions.rational(i32(5), i32(10))
+
+assert f.reduce().str() == '1000000000000000000000000000000/3'
+assert g.reduce().str() == '1/2'
+```