add jemallctl base; add trim to interface w/ console cmd

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/alloc/default.rs

@@ -1,5 +1,8 @@
 //! Default allocator with no special features
 
+/// Always returns Ok
+pub fn trim() -> crate::Result { Ok(()) }
+
 /// Always returns None
 #[must_use]
 pub fn memory_stats() -> Option<String> { None }