Add cal command (#1739)

* Add cal command

* Fix docmentation to show commands on two lines

* Use bullet points on flag documentation for cal

* Dereference day before calling string method

* Silence Clippy warning regarding a function with too many arguments

* Update cal flag descriptions and documentation

* Add some tests for the cal command

crates/nu-cli/tests/commands/mod.rs

@@ -1,5 +1,6 @@
 mod alias;
 mod append;
+mod cal;
 mod calc;
 mod cd;
 mod compact;