eva: add page (#3490)

pages/common/eva.md

@@ -0,0 +1,20 @@
+# eva
+
+> Simple calculator REPL, similar to `bc`, with syntax highlighting and persistent history.
+> More information <https://github.com/NerdyPepper/eva>.
+
+- Run the calculator in interactive mode:
+
+`eva`
+
+- Calculate the result of an expression:
+
+`eva "{{(1 + 2) * 2 ^ 2}}"`
+
+- Calculate an expression forcing the number of decimal places to 5:
+
+`eva --fix {{5}} "{{5 / 3}}"`
+
+- Calculate an expression with sine and cosine:
+
+`eva "{{sin(1) + cos(1)}}"`