Merge pull request #356 from igorshubovych/bc

bc: add calculator page

pages/common/bc.md

@@ -0,0 +1,19 @@
+# bc
+
+> Calculator.
+
+- Run calculator in interactive mode
+
+`bc -i`
+
+- Calculate the result of an expression
+
+`bc <<< "(1 + 2) * 2 ^ 2"`
+
+- Calculate with the given precision
+
+`bc <<< "scale=10; 5 / 3"`
+
+- Calculate expression with sine and cosine using mathlib
+
+`bc -l <<< "s(1) + c(1)"`